volume 26, issue 11 june 8, 2018 vegetable crops
TRANSCRIPT
June 8, 2018 Weekly Crop Update Volume 26, Issue 11 1
Volume 26, Issue 11 June 8, 2018
Vegetable Crops Vegetable Insect Update – June 8, 2018 – David Owens, Extension Entomologist, [email protected]
Beans Potato leaf hoppers are active in vegetables. Scout snap beans for nymphs and adults, by looking under leaves for the small, lime green, sideways-moving insects or by taking sweep net samples. Delaware thresholds are 5 per sweep; other states use a lower threshold closer to 1 adult per sweep.
Watermelon Striped cucumber beetles are still very active. Be on the lookout for them in recent transplants. Fields that have been recently treated with a neonicotinoid should still be giving control. Look for dead beetles on the leaves and beetles that are not moving or only slightly moving when prodded.
Foliar Fertilization of Vegetable Crops Revisited – Gordon Johnson, Extension Vegetable & Fruit Specialist; [email protected]
I recently looked a several vegetable plantings that showed severe damage from foliar fertilizers. The extended cloudy weather set up conditions where the plants were more susceptible to salt injury (thinner leaves with less developed waxy cuticles). With plant injury in mind, I thought it would be good to revisit the use of foliar fertilizers in vegetable crops.
Growers will apply most (>90%) of their plant nutrients for vegetable crops as soil applications (preplant, sidedressed, fertigated) based on soil tests and crop nitrogen needs.
To monitor vegetable nutrient status during the growing season, tissue testing is recommended just prior to critical growth stages. Growers can then add fertilizers to maintain adequate nutrient levels during the growing season or correct nutrient levels that are deficient or dropping.
Foliar fertilization is one tool to maintain or enhance plant nutritional status during the growing season. Often quick effects are seen and deficiencies can be corrected before yield or quality losses occur. Foliar fertilization also allows for multiple application timings post planting. In addition, there is reduced concern for nutrient loss, tie up, or fixation when compared to soil applications.
However, foliar fertilization has limitations. There is the potential to injure plants with fertilizer salts, application amounts are limited (only small amounts can be taken up through leaves at one time), multiple applications are often necessary (increasing application costs) and foliar applications are not always effective, depending on the nutrient targeted and plant growth stage.
Where foliar fertilization does have a good fit is for deficiency prevention or correction, particularly when root system function is impaired. This commonly occurs when there is extended rainy weather and soils are waterlogged. Foliar fertilization is also necessary
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when soil conditions, such as low pH, causes the tie up of nutrients so that soil uptake is limited. Foliar fertilization can also be used to target growth stages for improved vegetable nutrition thus improving color, appearance, quality, and yield.
Foliar fertilizers are applied as liquid solutions of water and the dissolved fertilizers in ion or small molecule form. Foliar nutrient entrance is mostly through the waxy cuticle, the protective layer that covers the epidermal cells of leaves. Research has shown that there is limited entrance through the stomata. While the waxy cuticle serves to control water loss from leaf surfaces, it does contain very small pores that allows some water and small solute molecules to enter the underlying leaf cells. These pores are lined with negative charges. Fertilizer nutrients in cation form or with neutral charges enter most readily through these channels: this includes ammonium, potassium, magnesium, and urea (NH4+, K+, Mg++, CH4N2O respectively). In contrast, negatively charged nutrients (phosphate-P, sulfate-S, molybdate-Mo) are much slower to move through the cuticle (they must be paired with a cation). Movement through the cuticle is also dependent on molecular size, nutrient concentration, time the nutrient is in solution on the leaf, whether the nutrient is in ionic or chelated form (complexed with an organic molecule), and the thickness of the leaf cuticle.
Another factor in foliar fertilizer effectiveness is what happens once the nutrient enters the leaf area. Some smaller molecules or those with less of a charge are readily transported in the vascular system to other areas of the plant (NH4+, K+, Mg++, Urea). Other larger molecules and more strongly positive charged nutrients stay near where they enter because they bind to the walls of cells in intercellular areas that contain negative charges. Tightly held nutrients include Calcium, Manganese, Iron, Zinc, and Copper (Ca++, Mn++, Fe++, Zn++, Cu++). Therefore, when applied as foliar fertilizers, calcium does not move much once it enters plant tissue, the negatively charged nutrients such as phosphorus and sulfur are very slow to enter the plant, and iron, manganese, copper, and zinc are slow entering and do not mobilize once in the plant.
The following is a list of the major plant nutrients that are effective as foliar applications, fertilizer forms best used for foliar applications, and recommended rates;
● Foliar applications of nitrogen (N) can benefit most vegetables if the plant is low in N. Urea forms of N are the most effective; methylene ureas and triazones are effective with less injury potential; and ammonium sulfate is also effective. Recommended rates are 1-10 lbs per acre.
● Foliar potassium (K) is used on fruiting vegetables such as tomatoes and melons. Best sources are potassium sulfate or potassium nitrate. Recommended rate is 4 lbs/a of K.
● Foliar magnesium (Mg) is used on tomatoes, melons, and beans commonly. The best source is magnesium sulfate and recommended rates are 0.5-2 lbs/a of Mg.
● Foliar calcium is often recommended, but because it moves very little, it must be applied at proper growth stages to be effective. For example, for reducing blossom end rot in tomato or pepper fruits, foliar calcium must be applied when fruits are very small. Best sources for foliar calcium are calcium nitrate (10-15 lbs/a), calcium chloride (5-8 lbs/a) and some chelated Ca products (manufacturers recommendations).
● Iron (Fe), manganese (Mn), or zinc (Zn) are best applied foliarly as sulfate forms. Rates are: Fe, Mn, 1-2 lbs/a, and Zn ¼ lb/a. While these metal micronutrients are not mobile, foliar applications are very effective at correcting local deficiencies in leaves.
● The other micronutrient that can be effective as a foliar application is boron. Boron in the Solubor form is often recommended at 0.1 to 0.25 lbs/a for mustard family crops such as cabbage as a foliar application. Boron is very toxic to plants if applied in excess so applying at correct rates is critical.
For foliar fertilizers to be most effective they should remain on leaves or other targeted plant tissue in liquid form as long as possible. Urea and ammonium nitrogen forms, potassium, and magnesium are normally absorbed within 12 hours. All other nutrients may take several days of wetting and rewetting to be absorbed.
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Therefore, it is recommended that foliar fertilizers be applied at dusk or early evening when dew is on the leaves, in high volume water, and using smaller droplets to cover more of the leaf. Applications should also be made when temperatures are moderate and wind is low. While foliar fertilizers are sometimes applied with pesticides, for best effectiveness and reduced phytotoxicity potential it is recommended that they be applied alone. Use only soluble grade fertilizers for foliar applications (many are already provided in liquid form) and adjust water pH so it is slightly acidic.
Foliar fertilizers are most effective when applied to younger leaves and fruits. Research has shown that as leaves or fruits age, cuticles thicken, and these thicker cuticles absorb significantly lower amounts of nutrients such as potassium. However, younger plant tissue is also the most susceptible to potential fertilizer burn.
Because foliar fertilizers are in salt forms they can damage plant tissue if applied at rates that are too high. Generally, a 0.5-2% fertilizer solution is recommended. Certain vegetables are more sensitive to fertilizer salt injury than others. Vegetables with large leaves with thinner cuticles (such as muskmelons) have greater risk of salt injury when compared to crops, such as cabbage, that have thick cuticles. Apply foliar fertilizers at recommended rates and dilutions for each specific vegetable crop.
In addition, some fertilizer sources are much more likely to cause injury than others. In the past this was given as the salt index for a fertilizer, the lower the salt index the less osmotic stress the fertilizer would place on the plant tissue. A better index would be the osmolality values for the fertilizer material. For foliar nitrogen materials, osmolality values (mmol/kg) for common N sources are as follows: Urea = 1018, UAN-28 = 1439, Ammonium sulfate = 2314, Potassium nitrate = 3434. This shows that potassium nitrate has over 3x the osmotic stress potential compared to urea when applied as a foliar fertilizer. This means that potassium nitrate has much more potential to cause salt injury to plants than urea and must be used at lower rates.
Revisiting Rainshelters for Vegetable and Fruit Production – Gordon Johnson, Extension Vegetable & Fruit Specialist; [email protected]
I had an interesting conversation with a Delmava-based crop consultant on the use of rainshelters for vegetable and fruit production. As the climate is expected to become wetter with more extreme rainfall events, losses of vegetable and fruits to excess rain will become more of a concern.
A rainshelter is a high tunnel structure that is used to cover plants during fruit formation and development. Multi-bay “European” style tunnels are most commonly used as rain shelters covering from ½ acre to several acres. Rain shelters are used extensively in high rainfall areas such as England to protect rainfall sensitive crops such as strawberries. Covers may be used for the whole season or just for the fruiting period.
Rainshelters are also used for tomatoes and other fruits such as cherries which are susceptible to cracking. Some fruits crack from absorbing water through the skin of the fruit when they are ripe or near ripe, others crack with excess water in the root zone, and there can be a combination of the two processes. Rainshelters control both types of fruit cracking. Rain shelters also reduce foliar wetting and rain splash and therefore can reduce fungal and bacterial diseases considerably if left on for the whole growing cycle.
While a high tunnel will serve as a rain shelter, less expensive low-tunnel structures can also be used that have a plastic cover over hoops from 2 to 6 feet tall.
Rain shelters have been shown to improve the quality of tomatoes throughout the growing season and can be a valuable tool to increased marketable fruits of high quality. They are also useful for fruit crops such as cherries, strawberries, brambles, grapes, and blueberries. Specialty melons prone to cracking will also benefit from the use of rainshelters.
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Dwarf cherries being grown under a rain shelter.
Seldom Seen Tomato Disease Found in High Tunnel – Jerry Brust, IPM Vegetable Specialist, University of Maryland; [email protected] and Karen Rane, UMD Plant Diagnostic Lab; [email protected]
A root disease that is most commonly associated with potato has turned up on tomato in a high tunnel last week. This disease goes by the delightful name of black dot root rot. The causal agent is Colletotrichum coccodes, which also causes anthracnose fruit rot on tomato (sunken, water-soaked, circular lesions).
C. coccodes infection on tomato roots appears as lesions on the root surface that produce black microsclerotia (the ‘black dot’ in its name) (Fig. 1). Infected plants will sometimes wilt, with the lower and middle leaves of the plant turning yellow.
C. coccodes has a very large host range, which includes members of Solanaceae, Cucurbitaceae and Leguminosae, both crops and weeds. Nightshade in particular (a solanaceous weed) can harbor the fungus, often without showing symptoms. The pathogen can survive in the soil for up to 8 years as microsclerotia.
This pathogen causes problems only under poor growing conditions or when other pathogens are present. The disease occurs in greenhouses or high tunnels where there has been a continuous cropping of tomato for several years, resulting in
very high levels of inoculum. Other conditions that can be encountered in high tunnels, such as high soluble salt levels, low pH, low or excessive fertilization, high temperatures and water stress, can predispose plants to infection and root rot by C. coccodes. These infected plants can at times show few symptoms, but still be responsible for yield reductions.
Management The disease can be prevented by growing in optimal conditions for tomato in the high tunnel. Deep plowing (12-15 inches, not easy to do in a high tunnel, we know) degrades infected plant debris more rapidly and buries propagules, both of which may help reduce fungal populations. Steam sterilization of the soil, or soil solarization for 8 weeks, can reduce disease incidence. Crop rotation is another tried and true management plan if growers can rotate out of any solanaceous, leguminous or cucurbit crops for 3-4 years — something most growers may not be able to accomplish. What may be the best solution for high tunnel growers with heavy inoculum levels of this disease is to move the high tunnel to different ground. Grafting is another possibility, but the plants in this high tunnel were grafted tomato plants, a different root stock may be resistant or more tolerant of the disease, but this is something that would need to be checked before using. Small grain or corn can be used in rotation in the field to reduce fungal populations.
Figure 1. Black dots (microsclerotia of C. coccodes) on tomato root
Vegetable Disease Update – June 8, 2018 – Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; [email protected]
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Scab of Cucurbits Cool wet weather is associated with several vegetable diseases. One of these is scab on cucurbits, caused by the fungus Cladosporium cucumerinum, which is favored by temperatures at or below 70°F and wet weather.
Watermelons are highly resistant to scab, and many cucumber cultivars also have resistance (see the Commercial Vegetable Recommendation Guide for a list of resistant cucumber varieties). However, summer and winter squash, pumpkin, gourds, muskmelon and honeydew are susceptible. Symptoms vary somewhat depending on the cucurbit crop. However, leaf lesions appear as water-soaked, pale green to grey or white and angular. Dead leaf tissue cracks and looks “ragged” and is sometimes referred to as shot-holed. Fruit may have sunken spots (summer squash or susceptible cucumber), or raised scabby lesions (butternut squash). Scab should be managed by using resistant cultivars when available, and rotating out of susceptible crops (cucurbits) for two years. Application of chlorothalonil is also effective.
Scab lesions on summer squash
Scab lesions on cantaloupe
Hop Downy Mildew Hop downy mildew was found near Wye Mills, MD on the Eastern Shore on Friday. Our weather remains very conducive for this disease which likes cool temperatures and high humidity. Symptoms are angular lesions on the leaves that are brown and necrotic. Image shows the upper surface of leaves with angular lesions caused by downy mildew. Sporulation occurs on the lower surface of the leaf.
Cucurbit Downy Mildew Please note that the pathogen that causes hop downy mildew is NOT the same as the one that causes cucurbit downy mildew. Cucurbit crops should be monitored for presence of downy mildew, however the closest reported outbreak of cucurbit downy mildew as of June 7, 2018 is in North Carolina.
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Image show a screen shot of current outbreaks of downy mildew in the eastern U.S. from the ipmPIPE website (http://cdm.ipmpipe.org/scripts/map.php). Red denotes counties where downy mildew was found in the last 7 days, and green counties represent outbreaks reported more than 7 days ago.
Be Alert for Late Blight Showing Up on Tomatoes – Jerry Brust, IPM Vegetable Specialist, University of Maryland; [email protected]
Another disease we might be seeing now and in the next week or so is late blight. The weather conditions of the past week have been favorable for its development: cool (for summer temperatures) daytime and nighttime temperatures along with ample moisture. It is important to watch for this disease and treat for it as soon as it is observed or is found in your area. Symptoms of late blight on tomato leaves are irregularly shaped water-soaked lesions that appear on young leaves at the top of the plant. Under humid conditions, these lesions become brown (Fig. 1a) and white fuzzy sporulation can be seen (Fig. 1b). Eventually the leaves shrivel and die. Brown lesions with sporulation also can occur on stems and leaf pedicels (Fig. 1c). The pathogen infects tomato fruit and causes circular greasy lesions. The fruit remains firm but can become leathery and dark brown. Best management practices for late blight control are found in the 2018 Mid-Atlantic Commercial
Vegetable Production Recommendations Guide found at: http://extension.udel.edu/ag/vegetable-fruit-resources/commercial-vegetable-production-recommendations/
Figure 1. Late blight lesion on tomato leaf (A), sporulation of late blight causing ‘fuzzy growth’ (B) and late blight lesion and sporulation on tomato stem (C).
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Agronomic Crops Agronomic Insect Update – June 8, 2018 – David Owens, Extension Entomologist, [email protected] and Bill Cissel, Extension Agent – Integrated Pest Management; [email protected]
Alfalfa Continue scouting for potato leaf hopper and hopper burn. Yellowing leaves are a sign that yield has been impacted. Thresholds are adjusted for plant height, the smaller the plant, the lower the threshold. As a general guide, use a threshold of 1 leafhopper in 5 sweeps for plants less than 3 inches tall and moving up to 1 leafhopper per sweep for plants greater than 7 inches.
Soybean Bean leaf beetles, grasshoppers, and thrips are active in fields. A couple of Mexican bean beetles have been spotted in New Castle County. Recent conversations with entomologists from the South have indicated that our early season defoliation thresholds are pretty conservative, although they are currently at 30% defoliation pre-bloom. Thrips feeding is generally only a problem with field wide averages of 8+ per leaflet and in dry years where the plants are under water stress, which is not this year.
Delaware Has Seen Variable Rainfall - Jarrod O. Miller, Extension Agronomist, [email protected]
Every spring has the same difficulties in not only getting seeds into the ground, but also protecting young plants from cold or moisture. The only thing that is the same every spring, is the difficulty in predicting the best time to plant. This year we saw a cool early April pushing back most corn planting until the 22nd, followed by high temperatures in early May.
Rainfall accumulations were fairly normal in April, with only 2-4 inches across Delaware over the entire month. Since then we have seen some fairly intense rainfall that has varied in
accumulation across the state. Selecting a few weather stations from the Delaware Environmental Observing System (DEOS-http://www.deos.udel.edu/) reveals that statewide variability, as our research station in Georgetown has seen almost 16 inches of rain since April 1st compared to the Newark campus with ten. Most of the rain has come in the second half of May, but each storm has randomly saturated a different part of the state.
Tackling the Nitrogen Dilemma in Corn - Amy Shober, Extension Specialist – Nutrient Management and Environmental Quality, University of Delaware, [email protected], Sydney Riggi, Extension Agent – Nutrient Management, University of Delaware, [email protected]; Jarrod Miller, Extension Specialist – Agronomy, University of Delaware, [email protected]; Phillip Sylvester, Extension Agent, University of Delaware, [email protected]; Karen Gartley, Soil Testing Program Director, University of Delaware, [email protected]
As we have highlighted in previous weeks, managing nitrogen (N) when it won’t stop raining is a difficult task. The PSNT is meant to help measure the N that is available from organic amendments, like animal manures. Organic forms of nitrogen and ammonium are rapidly converted by soil microbes to nitrate (NO3
-) once soil temperatures exceed 60°F, conditions we have observed since late April/early May. As such, we expect that organic forms of N, like those in animal manures, were converted to ammonium (NH4
+) earlier in the season. Once
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present as ammonium, conversion to nitrate by soil microbes is rapid (unless a nitrification inhibitor was applied to manure or soil). This nitrate was then susceptible to leaching below the root zone, runoff from fields where rainfall exceeded infiltration, or loss to the atmosphere from soils that were flooded for more than 48 hours.
We still advocate using a PSNT for fields with a recent history of manures or cover crops. However, the copious amounts of rain this year, coupled with rapid conversion of N in the soil, makes it difficult to rely solely on results of a PNST to determine your sidedress needs. Part of the difficulty we are having in making sidedress N recommendations this year is related to the huge variability in PSNT values we are seeing in fields with similar management. For example, we have received reports of pre-sidedress nitrate test (PSNT) values that are well below the 25 ppm NO3-N threshold (e.g., 8-10 ppm NO3-N) in soils that received moderate amounts of manure (e.g., 2-3 tons/ac) and commercial starter N fertilizers (30-80 lb/ac). However, we have also seen samples with PSNT values as high as 45 ppm NO3-N from nearby fields under the same management conditions. In a “normal year”, PSNT-based sidedress recommendations are determined by the concentration of nitrate in the PSNT sample, which is then adjusted for manure application (based on the timing and amount of manure applied) and any starter N applied prior to or at planting. But this year, Mother Nature is making it harder for us to make the call on if there is really manure N left to mineralize. We have also been measuring soil ammonium concentrations to look for evidence of delayed mineralization. Unfortunately, low soil ammonium concentrations (< 5 ppm) suggest that there is not much delay in the mineralization and that much of the organic N has been lost. As such, the University of Delaware Soil Testing Lab is recommending a range of sidedress N rates based on the PSNT.
Recognizing that N is important for adequate crop growth but that too much can result in environmental issues, we ask growers and consultants to consider the following before deciding exactly how much sidedress N to apply to corn (when you finally get out into the field):
1. Are there visible signs of significant crop stress that will likely reduce the chance of achieving your expected yield goal (e.g., poor stand uniformity, dead or dying plants, poor root development) or does your corn look pretty healthy (e.g., even stand, healthy green color, healthy roots)?
If you have poor stand uniformity or signs that plants were drowned out, this is a good indication that you may lose yield. In this case, we recommend that you reduce your yield goal and fertilize at a lower N rate. Remember, fertilizing dead or dying corn will not bring it back. In contrast, if your crop looks to be in pretty good shape, then you can consider adding N at a higher sidedress rate to account for early season N losses.
2. Will putting equipment into the field to sidedress cause more damage than it’s worth?
If you put equipment in the field while it is still too wet, you risk getting stuck and/or causing significant compaction. Both will cost you money and time to fix. If you can’t get equipment in the field before the corn is too tall, and you feel that you must get some N out, you have the option to fly on granular urea. While some sources recommend that you keep rates low (<60 lb/ac) to prevent leaf burn, research out the the University of Missouri suggests that applications of up to 150 lb/ac of urea are possible without significant leaf burn to the plant. If you do consider aerial urea application, you should consider that urea must be watered in (by rainfall or irrigation) to prevent significant ammonia volatilization; a urease inhibitor can help reduce ammonia loss, to some extent. The economics of aerial N applications should be considered before going this route.
3. Can you fertigate?
If you are set up to fertigate and you can get your pivot around without causing compaction or getting stuck, we recommend putting out a modest amount of N now, then take tissue test later in the season and, if needed, add more N through the irrigation system later in the season.
4. Will an additional N application cause you to add more than was in your nutrient management plan?
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In Delaware, you should contact your consultant to have them write a justification for additional fertilizer applications. A copy of the addendum should be included with the original nutrient management plan before the end of the calendar year and will be essential if the farm is audited. The Delaware Department of Agriculture can be contacted for guidance and clarification. Consultants and growers from other states should contact State regulatory agencies for guidance. Click here for Delaware Department of Agriculture contact information.
No-Till Soybeans Treated with Early Burndown Herbicides – Mark VanGessel, Extension Weed Specialist; [email protected]
Soybean fields treated before the rains that have not been planted yet are probably experiencing weed breaks. Even the least water-soluble herbicides have lost most of their herbicidal activity. Be sure to scout these fields and if there are emerged weeds at planting, be sure to control them. These fields will need a non-selective herbicide such as glyphosate or paraquat. The challenging scenario is if Palmer amaranth or horseweed are present along with grasses. Paraquat plus some metribuzin will control newly emerged Palmer amaranth or horseweed plants; and burn off the grasses but they will probably regrow if they are over 3 inches. While glyphosate will control the grasses, it will not kill the horseweed or Palmer amaranth. My advice is to focus on the biggest challenge, Palmer amaranth and horseweed and you can attack the grasses after the soybeans have emerged with glyphosate or Select or Poast or something similar.
Soil-applied herbicides generally do not control emerged weeds. However, we have had some success on 1 to 2 inch tall weeds with 3-4 oz of metribuzin plus 2 oz of Valor plus nitrogen plus crop oil. Be aware weeds over 2 inches may not be controlled, and this will not control emerged grasses or emerged horseweed. I am not ready to endorse this approach, but it is the only combination of residual herbicides that have provided acceptable burndown activity on some weed species.
The combination of metribuzin plus Valor with paraquat has looked very good in our trials for treating early burndown fields that needed retreating before planting. However, this combination may not be appropriate if you used metribuzin and/or Valor early preplant.
Considerations for Postemergence Corn Herbicides – Mark VanGessel, Extension Weed Specialist; [email protected]
Many corn fields need postemergence treatment for weeds, but it maybe a week or two before the corn starts to shade the row middles. In this case, select an herbicide that will provide some residual weed control. Liberty, glyphosate, dicamba, or Aim/Cadet will not provide residual control. Consider atrazine if the corn is less than 12 inches, or a product with mesotrione (Callisto), Capreno, or Impact/Armezon for broadleaves. If you expect grasses to be a problem, then products such as Halex GT, Armezon PRO, or Capreno will help with residual control. Other products are labeled for corn less than 12 inches tall; refer to the Mid-Atlantic Field Crop Weed Management Guide for a complete list.
Considerations for Postemergence Herbicides and Planting Cover Crops this Fall – Mark VanGessel, Extension Weed Specialist; [email protected]
Most of the herbicides we use in corn and soybeans are compatible with planting cereal rye cover crop in the late summer or fall. However, use of residual herbicides such as Dual, Zidua, Outlook, or Warrant postemergence could pose a risk; particularly if the cover crop is planted prior to mid-September. Broadleaf cover crops such as forage radish or legumes are more likely to show injury from herbicides, and the sooner after application these cover crops are seeded the greater the risk for injury. We have seen stunting in the forage radish from Valor or Spartan. Postemergence applications of ALS herbicides (Group 2) or fomesafen (Reflex or FlexStar) have the greatest risk of injuring forage radishes.
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Hairy vetch appears to be more tolerant of herbicide carryover than crimson clover. Halex, Zidua, and atrazine in corn and fomesafen, Warrant and ALS herbicides in soybeans are the greatest risk to crimson clover.
Irrigated fields allow more herbicide degradation by microbes and less the risk of injury. Herbicide evaluation for carryover to cover crops is still an active area of research at UD and other universities and with more research, we hope to provide detailed guidance on this topic. However, if cover crops are an important part of your cropping system, give careful thought to the herbicides you use this spring to reduce the risk of cover crop injury this fall.
General Keep an Eye Out for Green Stink Bugs – Bill Cissel, Extension Agent – Integrated Pest Management; [email protected] and David Owens, Extension Entomologist, [email protected]
We have recently captured a large number of green stink bug adults in our black light traps. While there are no established thresholds or recommendations based on trap catches for stink bugs, this does alert us to the fact that adult activity is elevated and that green stink bugs may be moving into crops.
In Delaware, we have three species of stink bugs; green, brown, and the invasive brown marmorated stink bug that we monitor using black light traps. All three species of stink bugs are considered polyphagous, meaning they feed on many different crops. In general, we think of them as being “seed” feeders because they use their piercing-sucking mouthparts to feed on developing seeds, pods, and fruit. Stink bugs are very good at locating preferred food sources and move throughout the landscape, keying in on host plants that are in the optimum plant growth stage (i.e. plants in reproductive growth stages). Early in the growing season, tree fruit, early planted sweet corn, and plants in natural areas that are producing seeds and fruit are most attractive to stink bugs.
However, stink bugs have also been known to occasionally feed on corn seedlings, causing the plants to tiller as seen in the photo below.
Brown stink bug feeding injury
Stink bug injury on corn seedlings is more common in states to our south and usually is not something that we need to manage. But with the high number of green stink bugs captured recently, and many fields with corn in growth stages vulnerable to injury (V1-V6), keep an eye out for green stink bugs moving into seedling corn fields.
Curious about how active adult stink bugs are in your neck of the woods? Click on the link below to view our Insect Trap Catch webpage and then click on the link to the stink bug trap catch page where we post trap catch results: http://extension.udel.edu/ag/insect-management/insect-trapping-program/
If you want to compare current stink bug trap catches to previous years, click on the “historical interactive graph” link at the top of the page and then select a trapping location and stink bug species. Once you have selected a trapping location and stink bug species, historical trap catch results will be visually displayed as an interactive graph. Clicking on the years will disable them and you can click and drag to zoom.
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Recent research from North Carolina suggests that to sample seedling corn for stink bugs, sample at least 100 plants randomly throughout the field. Stink bugs usually are more concentrated on field edges so concentrate scouting efforts there first. If you find high levels of stink bugs on the field edge, make sure you are also sampling the field interiors.
Two new thresholds have been developed based on the sampling method, partial and entire plant. The partial plant method is based on only sampling a portion of the plant and recording the number of stink bugs per 100 plants. The entire plant sample is based on the percent of infested plants, visually searching the entire plant for stink bugs.
The partial plant threshold that were recently developed in North Carolina for stink bugs is as follows for field corn V1-V6 only sampling the stalk below the lowest green leaf:
● 6 stink bugs per 100 plants or fewer, do not treat.
● 13 or more stink bugs per 100 plants, treat.
● If the number of stink bugs per 100 plants is between 6 and 13, treat if you have 9 or more bugs per 100 plants.
If you sample the entire plant, the threshold that is being recommended in North Carolina is as follows for field corn V1-V6:
● <6% of the plants infested, do not treat.
● >11% of the plants infested, treat.
● If the % of the plants infested falls between 6-11%, treat if 8% or more of the plants are infested.
It should be noted that this threshold was recently published and has not been evaluated in Delaware.
Here is a link for more information on how to use the new stink bug threshold that was developed in North Carolina: https://entomology.ces.ncsu.edu/2018/04/new-stink-bug-thresholds-in-corn/
Guess the Pest! Week #10 Answer: Stagonospora nodorum Leaf Blight and Glume Blotch - Bill Cissel, Extension Agent – Integrated Pest Management; [email protected]
Congratulations to Buzz Lowe for correctly identifying the disease in the photo as Stagonospora nodorum leaf blight and glume blotch and for being selected to be entered into the end of season raffle for $100 not once but five times. Everyone else who guessed correctly will also have their name entered into the raffle. Click on the Guess the Pest logo to participate in this week’s Guess the Pest challenge!
Stagonospora nodorum Leaf Blight and Glume Blotch By Nancy Gregory
Stagonospora nodorum leaf blight and glume blotch can cause yield loss on wheat, especially if infection occurs before grain fill. Stagonospora overwinters in crop residue and can be spread in infected seed. Disease is favored by environmental conditions of high moisture and wind, resulting in spore movement up through the canopy. Disease spread slows when weather turns dry. Symptoms include oval to round, brown leaf spots with yellow halos. The glume blotch phase is characterized by gray to purple brown discoloration on the outer seed coverings. Closer look with a hand lens may show a dusty cast to the heads when the fungus is producing spores. Management strategies include rotation to soybean, corn, or other on-hosts, as well as proper plant density to avoid over-crowding. Fungicide applications of a labeled triazole or
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strobilurin product at heading can be a part of a management plan. Resistant varieties are available for fields with a known history of glume blotch.
Guess the Pest! Week #11 – Bill Cissel, Extension Agent – Integrated Pest Management; [email protected]
Test your pest management knowledge by clicking on the GUESS THE PEST logo and submitting your best guess. For the 2018 season, we will have an “end of season” raffle for a $100.00 gift card. Each week, one lucky winner will also be selected for a prize and have their name entered not once but five times into the end of season raffle.
This week, one lucky participant will also win A Farmer’s Guide To Corn Diseases ($29.95 value).
You can’t win if you don’t play!
What caused this damage?
Loss Adjustment Procedures for Fumonisin - Compiled by Lucas Clifton, Program Specialist, Targeted States RME, [email protected]
Fumonisin contamination can be harmful to humans and animals at certain levels. The U.S. Food and Drug Administration (FDA) has established action levels for Fumonisin present in food or animal feed. Post-harvest Fumonisin contamination can increase during storage and if crop drying is delayed. The commodities with the highest risk of Fumonisin contamination are corn, peanuts, and cottonseed.
The FDA has no published action levels or use restrictions for crops with zero to 2.0 parts per million (ppm) of Fumonisin. Therefore, crop insurance policy provisions do not provide quality adjustments for levels below 2.1 ppm.
If you think your insured crop has Fumonisin, contact your crop insurance agent before you:
• Harvest the grain; • Put the grain in storage; or • Deliver it for sale.
Your insurance provider will:
• Take samples for testing; and • Submit them to an approved Fumonisin
testing facility. • Cumulative or blended samples are allowed
by unit in accordance with procedures.
Criteria for Approved Testing Facilities Contact your agent or refer to the applicable special provisions for the most current policy on testing.
Testing facilities meeting the criteria below can be considered “approved testing facilities” for crop insurance:
• An approved testing facility must be able to perform quantitative tests on grain, itemizing results in parts per billion. Test kits used must be certified by the USDA Grain Inspection, Packers and Stockyards Administration (GIPSA);
• The facility must be a recognized commercial, government, or university testing lab that uses industry recognized
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sample sizes, equipment, and procedures for testing Fumonisin.;
• The facility must be a disinterested testing facility; and
• The facility must not be involved in buying or selling the type of grain that is being tested.
Talk to your approved insurance provider (AIP) or agent for more information. Visit www.gipsa.usda.gov/fgis/serviceproviders_listing.aspx for approved testing facilities.
Because Fumonisin under some conditions (high moisture) can worsen in storage, Fumonisin losses are only insurable if:
• The grain is tested at an approved testing facility before being moved into commercial or on-farm storage; or
• Your AIP asks you to leave representative sample areas of the unharvested crop for taking samples for testing.
Losses not covered under the crop insurance policy include:
• Losses due to an increase in the Fumonisin level while in farm or commercial storage; and
• Losses that cannot be determined because proper testing was not completed.
The FDA, or another government agency, may require the destruction of crops with more than 100 ppm. If you destroy the crop in an acceptable manner, you will be paid a full loss. Please contact your AIP about acceptable ways to destroy your crop before doing so.
Quality Adjustment If the crop qualifies for quality adjustment (test results are 2.1 ppm and above), you may receive the actual Reduction In Value (RIV) if:
• The RIV is due to an allowable quality deficiency.
• You deliver and sell your crop to a buyer directly from the field; or
• You put it in commercial storage without the crop going into on-farm storage and the crop is sold not later than 59 days after the calendar date of the end of the insurance period to a disinterested third party.
Claims are not settled for production that contains levels of Fumonisin over the maximum amounts (100.0 ppm) shown in the special provisions (part of your insurance policy) until the crop is sold to a disinterested third party, fed, used, or destroyed.
If you are concerned about placing Fumonisin-infected grain in storage or about efforts to reduce the spread of Fumonisin within grain storage facilities, you should contact your AIP or local agricultural experts. You should contact your crop insurance agent, AIP, or applicable RMA Regional Office if you have questions about your crop insurance coverage.
Announcements
Poultry Grower Basics: Neighbor Relations, BMPs and Warm
Weather Ventilation
Monday June 11, 2018 1:00 p.m. – 3:15 p.m.
UD Carvel Research & Education Center 16483 County Seat Hwy, Georgetown, DE
Monday June 11, 2018 6:00 p.m. – 8:15 p.m. UD Paradee Center
69 Transportation Circle, Dover, DE
Nutrient Management Credits: 2.25
Registration Required: To register please contact Terra Eby at 302-735-8137 or [email protected]
June 8, 2018 Weekly Crop Update Volume 26, Issue 11 14
2018 Delaware Cooperative Extension Horticulture Short Courses
Register for this course online.
Pest and Beneficial Insect Walk $15, 2 Pest., 1 CNP, 2 ISA credits Wednesday, June 20, 4-6 pm University of Delaware Botanic Gardens 531 S College Avenue, Newark, Meet at the entrance to Fischer Greenhouse. Learn to identify insect and disease pests, as well as beneficial insects in the landscape at either the Sussex County Extension Office or the University of Delaware Botanic Gardens. Instructors: Nancy Gregory, Brian Kunkel, Carrie Murphy, and Tracy Wootten
2018 UD Weed Science Field Day Wednesday, June 20, 2018 8:30 a.m. University of Delaware Carvel Research and Education Center 16483 County Seat Hwy, Georgetown, DE
The UD Weed Science Field Day will begin with registration at 8:30 at the Grove near the farm buildings and new office building on the north side of the road. We will start to view the plots at 8:45 am.
The weather has been a challenge to get plots planted. All of our corn studies will be part of the tour, which includes most of the commercially available herbicides. Some of corn trials include different approaches and timings of herbicide application. Most of our soybean trials were recently planted, but we will view various burndown trials for full-season no-till production. We will also talk about the various cover crop trials. Our trials with Xtend soybeans, Liberty Link, and Enlist soybeans will not be at a stage to view until later this summer.
Coffee, juices, and donuts will be provided. We will also provide sandwiches for lunch.
Pesticide credits and Certified Crop Advisor continuation credits will also be available.
Dr. Michael Flessner, VA Tech, will hold a field day on Tuesday, June 19th at Blackstone, VA
Dwight Lingenfelter, Penn State, will hold a field day on Thursday, June 21st at Landisville, PA
2018 Farmers’ Field Day At LESREC
Wednesday, June 27, 2018 9:00 a.m.-1:00 p.m. University of Maryland
Lower Eastern Shore Research & Education Center (LESREC)
27664 Nanticoke Road, Salisbury, MD 21801
Calling all Farmers/Growers to Your Field Day at LESREC
Topics • IR-4 Program • Nutrient Management & Soil Health • Ag Law and Conserve (Possible Nutrient Mgmt. Credits) • Plant Pathology Information • Variety Studies • Weed Management • Poultry Information • Diagnostic Information • Bee / Pollen Research • Wagon Tours
Lunch will be provided
REGISTER AT: https://2018-farmers-field-day-at-lesrec.eventbrite.com
More Information to Follow. Check out Events at https://extension.umd.edu/lesrec
The University of Maryland is an Equal Opportunity Employer and Equal Access Programs
Blueberry Experimental Plot Tour Tuesday, June 26, 2018 6:00-8:00 p.m.
University of Delaware Carvel Research & Education Center
16483 County Seat Highway Georgetown, DE 19947
This meeting will highlight variety testing and other research with blueberries.
This is the last season that we will be maintaining and collecting data from the blueberry experimental planting at the research farm. Come see and taste the 25 varieties in the variety trial!
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Tour the blueberry variety trial, fertilization and soil amendment experiments.
The meeting will conclude with an ice cream and berry treat.
Please pre-register by June 25 by contacting Karen Adams at (302) 856-7303 or [email protected].
Weather Summary Carvel Research and Education Center Georgetown, DE
Week of June 1 to June 7, 2018 Readings Taken from Midnight to Midnight
Rainfall: 0.09 inch: June 1 0.96 inch: June 3 0.04 inch: June 4 Air Temperature: Highs ranged from 86°F on June 1 to 71°F on June 6. Lows ranged from 70°F on June 2 to 55°F on June 4 Soil Temperature: 70.9°F average
Additional Delaware weather data is available at http://www.deos.udel.edu/monthly_retrieval.html
and http://www.rec.udel.edu/TopLevel/Weather.htm
Weekly Crop Update is compiled and edited by Emmalea Ernest, Associate Scientist – Vegetable Crops University of Delaware Cooperative Extension in accordance with Federal civil rights law and U.S. Department of Agriculture (USDA) civil rights regulations and policies, the USDA, its Agencies, offices, and employees, and institutions participating in or administering USDA programs are prohibited from discriminating based on race, color, national origin, religion, sex, gender identity (including gender expression), sexual orientation, disability, age, marital status, family/parental status, income derived from a public assistance program, political beliefs, or reprisal or retaliation for prior civil rights activity, in any program or activity conducted or funded by USDA (not all bases apply to all programs). Remedies and complaint filing deadlines vary by program or incident. Reference to commercial products or trade names does not imply endorsement by University of Delaware Cooperative Extension or bias against those not mentioned.