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Issue: 17-13October 20, 2017

In This IssueCrop ConditionsLate Season Leaf Diseases of GrapesCrown Gall of Grape VinesWill Low Tunnels Provide New Opportunitiesfor Strawberry Production in Indiana?Rot ReduxUpcoming Events

Crop ConditionsApple harvest is winding down with late varietiessuch as GoldRush and Pink Lady being harvested.Quality has continued to be good, although somestem-end cracking has shown up on somecultivars. We have continued to run about a weekearly throughout the season.

Late Season Leaf Diseases ofGrapesPowdery and downy mildew can develop ongrapes in the late season, post harvest. It isimportant to keep vines as healthy as possiblegoing into winter. With the long fall we areexperiencing, downy and powdery mildew areboth becoming prevalent in many vineyards.Growers should consider a late seasonapplication of fungicides to keep these diseasesunder control to protect the foliage and assureadequate cold acclimation. Downy can becontrolled with phosphorous acid products,mancozeb, or captan. However, none of those

fungicides will control powdery mildew. So a tankmix including one of the above with a sterolinhibitor such as Rally or Tebuzol would be agood approach.

Powdery mildew on grape leaf

Downy mildew (and powdery

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mildew) on grape leaves

Crown Gall of Grape VinesCrown gall is a common disease of manyperennial plants. It causes fleshy tumors todevelop on the plant and usually results in plantdeath. Grapes are among the most sensitive fruitcrop to crown gall.The disease is caused by the bacteriumAgrobacterium tumefaciens. This is the samebacterium that is used to genetically modifyimportant crops. There are at least three biovarsof A. tumefaciens that cause crown gall. Theparticular strain that infects grapes is biovar 3.This strain was renamed Agrobacterium vitissince it only infects grape vines and closerelatives.The life cycle of Agrobacterium is interesting. Thebacterial cells infect the plant through wounds.These can be caused by insects, mechanicaldamage, or in the case of grape vines, coldinjury. Once the tissue is damaged, the bacterialcells can attach to the plant cells. However,rather than causing a canker or rot by replicatinginside the plant tissue, the bacteria release atumor-inducing plasmid, or circular piece of DNA,into the plant cell. It is this TI plasmid thatcauses the plant to react. The DNA from theplasmid gets inserted into the plant genome andinfected cells begin to divide and proliferaterapidly, producing callous tissue that forms thegalls that are visible on the plant surface. Therapid proliferation of callous disrupts the vasculartissue at the site of the gall and causes areduction in water and nutrient movement in theplant. Infected plants typically die from a type ofinduced water and nutrient stress.Starting with clean plant material is the bestmethod of avoiding crown gall. Planting on welldrained soils is also important. Once infected,

plants cannot be cured. However, bringing upnew shoots from below the gall to establish newtrunks is one method of managing crown galldisease. Often the plants must be completelyreplaced. Economic losses to crown gall can besignificant when cold tender cultivars are grownin regions where cold injury is likely.

Crown gall on grape trunk

Will Low Tunnels Provide NewOpportunities for StrawberryProduction in Indiana?Strawberry production in Indiana primarilyutilizes the matted row system in which bare rootstrawberry plants are set in the spring, fruit isfirst harvested in the second year and plants aremaintained for a few seasons. Strawberryproduction using an annual plasticulture systemis popular in the southern states, wherestrawberries are planted in the fall and harvestedin the next spring. In the annual plasticulturesystem, strawberries have a longer harvestperiod and produce fruit with better quality.Growing strawberries as an annual crop is achallenge in Indiana. This is because our shortfall makes it difficult for plants to reach thedesirable size that leads to a sufficient yield in

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the following spring. This situation can bechanged with the use of high tunnels that provideadditional heat units and moderate frostprotection. In a trial conducted in a 30 ×96 hightunnel at Southwest Purdue Ag Center,strawberries were planted in Sep. 2015. Themajority of strawberries were harvested in Apriland May 2016. A total yield of 1,295 lbs ofstrawberries were harvested from the 0.07 acrearea, which is very promising. However, werealize that space in high tunnel is extremelyvaluable. We have to consider high tunnelreturns on a per square foot, and a per monthbasis. In this regard, strawberries that take eightmonths from planting to harvesting may not bethe top crop to achieve the best returns. If agrower only has one or two 4-season hightunnels, strawberry is probably not

Strawberryproduction

Strawberryproduction

he top choice of crops.With these considerations in mind, we initiated anew project to evaluate another system to growstrawberries, the retractable low tunnel system.This system requires an initial investment aboutone third the cost of a high tunnel. We plantedstrawberries on Sep. 13 of this year. The lowtunnel was set up on Oct. 6. Eight varieties arebeing grown side-by-side under low tunnels andthe open field. We are going to compare effects

of the heat accumulation under low tunnels withopen-field on strawberry growth and yield. Wewill also compare effects of frost protection oftraditional straw mulch with fabric row covers inthe winter. Updates about the trials will bepublished on Facts for Fancy Fruit and VegetableCrops Hotline Newsletters over the next fewmonths. Please follow us to learn more aboutusing the low-tunnel system for growingstrawberries in Indiana.

Rot ReduxSummer rots continue to rear their ugly heads(Fig. 1). This year, we are even seeing them onlate season apples like Evercrisp (Fig 2) andGoldRush.On the plus side, we are seeing some level ofcontrol with all fungicides in our trials (data willbe presented at the Indiana Hort Congress);unfortunately, on highly susceptible varieties likeHoneycrisp, we need to do more research tofigure out how to better control these pathogens.Treatments that provided reasonable control inGolden Delicious suffered 10 times moreinfections on Honeycrisp. Future research willexamine the role of timing and fungicide choiceon infection.As always, please contact me if you are seeingnew problems, increasing severity of problems,or you can surprise me and tell me what a greatyear you had! As you can see, Jojen loved theharvest, and has decided like most children, thatHoneycrisp and Evercrisp are his favorite apples,followed by Golden Delicious (Fig. 3).

Fig 1 White rot(left) and bitter

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rot (right)

Fig 3 Jojen giveshis approval but

really wantedHoneycrisp,

instead

Fig 2 Evercrisp,sack of apple

sauce,compliments of

white rot

Upcoming EventsIndiana Horticultural CongressFebruary 13-15, 2018Indianapolis Marriott East Indianapolis, INContact Lori Jolly-Brown@ljollybr@purdue.eduVisit www.inhortcongress.org for more details

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