Integrated Disease Management

Disease Resistance and Cultural Controls

Fungicides

Disease Resistance

Environmental Manipulation

DiseaseManagement

Host Nutrition

Disease Management TriangleNow that we’ve covered fungicides let’s turn to the Host side of the Disease Management Triangle and discuss Disease Resistance and Host Nutrition

1. What is disease resistance? 2. Why is it important to consider disease resistance when selecting a turfgrass species and/or cultivar for a particular use and site?3. What impact do major and minor nutrients have on turf disease?4. What are some examples of disease suppression through environmental manipulation?5. Be prepared to draw disease triangles and disease management triangles for each of the diseases covered in the following sections.

Knowledge RequirementsWhen you complete this section, you should be able to answer these questions

DISEASE RESISTANCE

Disease resistance is a genetically controlled,physiological response of a host plant to a pathogen that limits disease severity or incidence.

DISEASE RESISTANCE1. Some species of turfgrass are more resistant to particular diseases than other species. Examples:

Anthracnose is severeonly on bentgrass andannual bluegrass.

Spring dead spot is severeonly on bermudagrass.

Gray leaf spot is commonon St. Augustinegrass,tall fescue, and perennialrye, but not on other grasses.

DISEASE RESISTANCE2. Some cultivars within a species are more resistant to particular diseases than other cultivars. Examples:

Tall fescue cultivars thatdiffer in susceptibilityto leaf blotch

Bluegrass cultivars thatdiffer in susceptibilityto leaf rust

Differences in pink patch amongryegrass cultivars

Susceptible

Resistant

Fungicides

Host Resistance

Environmental Manipulation

DiseaseManagement

Host Nutrition

Disease Management Triangle

Disease Management through Manipulation of Host Nutrition

1. Most info. on the effects of host nutrition on disease deals with nitrogen.

NITROGEN

Disease Management through Manipulation of Host Nutrition

1. Most info. on effects of host nutrition on disease deals with nitrogen.

2. Nitrogen enhances certain diseases (e.g. Pythium blight, spring dead spot, brown patch) and it suppresses other diseases (e.g. dollar spot, anthracnose).

NITROGEN

Disease Management through Manipulation of Host Nutrition

Enhancement of Disease by Nitrogen

1. Nitrogen enhances some foliar diseases (eg. Pythium blight, brown patch) by promoting the rapid production of young leaf tissue that is less resistant to fungal enzymes and toxins than older tissue.

Disease Management through Manipulation of Host Nutrition

Enhancement of Disease by Nitrogen

1. Nitrogen enhances some foliar diseases (eg. gray leaf spot, Fusarium patch) by promoting the rapid production of young leaf tissue that is less resistant to fungal enzymes and toxins than older tissue.

2. Nitrogen enhances root diseases by inhibiting root production in cool-season grasses, or by stressing roots through the production of excessive foliage in cool- and warm-season grasses.

Disease Management through Manipulation of Host Nutrition

Suppression of Disease by Nitrogen

Nitrogen can suppress certain diseases (eg. dollar spot, anthracnose) by inhibiting leaf senescence (aging).

Leaf senescence is commonin older leaves of turfgassplants. These senescing leavesare more susceptible to certainpathogens than non-senescingleaves. Nitrogen applicationscan delay leaf senescence,thereby reducing certaindiseases. Examples: dollar spotand anthracnose.

Senescing leaves

Disease Management through Manipulation of Host Nutrition

Suppression of Disease by Nitrogen

Nitrogen can suppress certain diseases (eg. dollar spot, anthracnose) by inhibiting leaf senescence

stimulating leaf growth to the extent that diseased portions of leaves are mowed off (e.g. dollar spot, red thread, leaf rust).

or by

Disease Management through Manipulation of Host Nutrition

POTASSIUM (K)

1. Some research suggests that K suppresses a few diseases (eg. snow molds) but evidence is not strong.

Disease Management through Manipulation of Host Nutrition

POTASSIUM (K)

1. Some research suggests that K suppresses a few diseases (eg. snow molds) but results are not extensive.

2. K is considered an element that will increase turfgrass tolerance to stress (heat, drought, disease, etc.). However, K should only be applied according to soil test results. High applications of K may result in salt injury to turf.

Disease Management through Manipulation

of Host Nutrition

Phosphorus (P)

There is no direct information indicating that P suppresses disease symptoms. However, Pmay enhance tolerance to root diseasesthrough its positive effects on root growth inyoung plants.

Disease Management through Manipulation

of Host Nutrition

Minor Elements

There is very little information on the effects of minor elements on turf disease.

Some evidence suggests that Mn and Zn aresuppressive to Take-All Patch and Take-AllRoot Rot.

(Fe, Mn, Zn, Cu, Mo, B, Cl)

Fungicides

Host Resistance

Environmental Manipulation

DiseaseManagement Host Nutrition

Disease Management TriangleA review of the Environmental Manipulation side of the Triangle

Disease Management through Environmental Manipulation

Examples

1. Reduction in the duration of leaf wetness will reduce severity of most foliar diseases of turfgrasses. This can be accomplished by:

A. Reducing shade – eg. removing or trimming trees and shrubs. B. Increasing air circulation – eg. using fans to

dry turf. C. Avoiding irrigation in late afternoon and early evening – This will allow turf leaves to dry before nightfall.

Disease Management through Environmental Manipulation

Examples

2. Increasing soil pH with lime or decreasing pH with ammonium sulfate may suppress certain diseases of turfgrasses. For example, the acidifying effect of ammonium sulfate suppresses the growth of the fungi that cause take-all patch of bentgrass and spring dead spot of bermudagrass.

Disease Management through Environmental Manipulation

Examples

3. Reducing soil compaction and thatch will limit the severity of virtually every turfgrass disease. “Soil compaction and thatch are the ‘cholesterol and fat’ of turfgrass health”

You should now be familiar with the basic components ofa Disease Triangle and a Disease Management Triangle. Thefollowing images are examples of each.

Gaeumannomyces graminis Creeping bentgrass

Take-All Patch

Soil temp. 40-60°FSoil pH >6.2High soil moisture

Example of a Disease Triangle

Name of diseaseName of pathogen

Name of host(s)

Environmental factors required for disease to develop

fenarimol,azoxystrobin

Take-All Patch

Species other than bentgrassare resistant. Bentgrasscultivars with someresistance include Regent,Procup, Putter.

Decrease soil pH with ammoniumsulfate; avoid use of lime; improvesoil drainage.

Increasing N cansuppress foliar symptoms. Increasing soil Mn can suppress root symptoms.

Example of a Disease Management Triangle

Fungicides registeredfor control

Disease Resistance

Host Nutrition

Environmental Manipulation

End of IDM - Disease Resistance and Cultural Controls