Be on the Lookout for Early Season Diseases of Small Grains

By Jaime Cummings and Ken Wise, NYS IPM

Winter wheat tillers
Winter wheat forming tillers on April 25th in Aurora, NY (photo by Jaime Cummings, NYS IPM)

With spring underway, our fall planted wheat, barley, rye and triticale crops have woken up and are in early developmental stages, and some spring planted barley, oats and rye are emerging.  By now, you’ve already assessed plant stands for winterkill or other weather-related damage and weed pressure.  But did you look for signs of diseases?

Fungicidal seed treatments protect our small grains crops from soilborne pathogens that cause damping-off, and foliar fungicides may be warranted for many of our common early-season foliar diseases.  Early epidemics from these pathogens may spread throughout the canopy as the season progresses, given favorable weather conditions, resulting in potential yield reductions.  An integrated approach for managing these diseases involves crop rotation, residue management, planting pathogen-free seed of resistant varieties, proper fertility and canopy management, and foliar fungicide applications where necessary.  Susceptible cultivars benefit most from fungicide applications for reduction of diseases.  While scouting, keep an eye out for some of our most common early season diseases:

Powdery Mildew can be commonly found lower in the canopy of all small grain crops, and is easily identifiable by its white, fuzzy fungal growth on both the upper and lower leaf surfaces (Fig. 1).  This pathogen overwinters on straw residues which provide inoculum in the spring to blow into growing wheat stands.  Cultivars vary in their levels of resistance to powdery mildew, and resistance is the most cost-effective method of defense.  Should you find high levels of powdery mildew in your field, you may consider a triazole foliar fungicide application at flag leaf emergence.

Powdery mildew of wheat
Figure 1. Powdery mildew of wheat (photo by Ken Wise, NYS IPM).

Septoria and Stagonospora Leaf Blotches are two other very common foliar diseases you may encounter in NY wheat fields.  Though caused by two different pathogens, the leaf spot symptoms can be somewhat similar and difficult to differentiate for scouts (Fig. 2).  Both fungal pathogens overwinter on crop residues, and initial infection often occurs on seedlings emerging in the fall, but may also occur in the spring.  Many commercially available cultivars are available with varying levels of resistance to these pathogens.  But if you notice high levels of leaf blotches in your field, you may consider a foliar application of a strobilurin or triazole fungicide at flag leaf emergence to protect yield.

Stagonospora leaf blotch of weat
Figure 2. Stagonospora leaf blotch of wheat (photo by Ken Wise, NYS IPM).

Leaf Rust, or brown rust, can occasionally be found early in the season, though it often appears later as the spores migrate on winds from the south.  Leaf rust is easily identified as bright orange pustules on the upper leaf surfaces throughout the canopy of all small grain crops (Fig. 3).  Rust fungi are obligate pathogens, which require a living host, and therefore must either over-winter on alternate hosts, or arrive on wind currents from the south.  Planting resistant cultivars is the most cost-effective management tool, and a flag leaf application of a strobilurin or triazole fungicide also offers effective control of leaf rust on susceptible cultivars.

Wheat leaf rust
Figure 3. Wheat leaf rust (photo by Ken Wise, NYS IPM).

Scald is another fungal leaf spot that easily identified on winter malting barley by its distinctive lesions that can be found on any above-ground plant tissue (Fig. 4).  The fungal pathogen can over-winter on residues or can be seed-transmitted.  On susceptible cultivars and under favorable environmental conditions, scald can spread quickly throughout the canopy and field, resulting in significant yield loss.  Pay attention to scald resistance ratings when selecting malting barley cultivars to plant, as they vary drastically in susceptibility.  Susceptible cultivars will benefit from a triazole fungicide application at flag leaf, or even earlier to protect yields.

Scald on malting barley
Figure 4. Scald on malting barley (photo by Jenn Thomas-Murphy, Cornell University).

When deciding whether or not to spray a fungicide, there are many points to consider.  Not least of all, cost.  Use the following information as a guide from the Cornell Integrated Guide for Field Crop Management for making fungicide decisions in small grains:

Activity Worksheet: Economical Analysis of Thresholds in Wheat:

Does the crop have a reasonable yield potential?

Assess the crop in early May (stem elongation stages) for adequate stand (density of approximately 30 strong stems per foot of row for 7-inch rows on good soils) and plant vigor. If the stand is sparse or plants are not vigorous or show widespread virus symptoms, fungicide application should not be considered further.  ____ Yes    ___ No

Have foliar diseases been observed before flag (last) leaf emergence?

Assess upper three leaves for symptoms and signs of powdery mildew, leaf spots, or leaf rust in early to mid-May, before flag leaf emergence. If disease (any amount) is observed on approximately 50 percent of main tillers, averaged across the field, a spray should be considered now. This threshold is exceeded in less than 50 percent of location/year situations in New York, so there is a significant risk of making an unnecessary fungicide application.   ____ Yes   ___ No

Have foliar diseases been observed during head emergence?

Assess upper two leaves for foliar diseases in late May to early June; if disease (any amount) is observed on approximately 50 percent of main tillers, a spray should be considered now. Fungicide applications made after early June may control some diseases but are unlikely to produce significant yield benefits.  ___ Yes  ___ No

Are climatic predictions conducive for further disease development?

Powdery mildew development is reduced dramatically once the average daily temperature rises above 70˚F; this disease often disappears by June. Severe leaf spot development is favored by extended periods of wet weather; it may be insignificant if dry weather persists in May and June. Listen for regional advisories on the threat from leaf rust; rust inoculum often builds up in areas to the south and west of New York and is deposited here by thunderstorms in June or July. In addition to disease observations, use long-range local weather forecasts in making your spray decision.  What is your short to medium term weather conditions?

Have I selected fungicides appropriate for the disease spectrum and have I read the label carefully?

Be sure that the materials you spray will be effective against the range of diseases found in your field; e.g., some products effective against powdery mildew are ineffective against leaf spots or vice versa. Check in the Cornell University Guide for Integrated Crop Management.

Is the spray decision consistent with my perception of risk?

A simple formula for evaluating the relative economics of a fungicide spray is: Relative Profit = (Grain Yield Increase x Grain Price) – (Cost of Fungicide + Application Costs). If ground spray rigs are used, the yield lost to wheel traffic should also be factored in. Each of these variables influences the relative economics of fungicide application. At a grain price of $4, producers will need to see approximately a 5 bu/A yield increase to break even on the added costs of fungicide application. Because disease occurrence is erratic over years and locations, fungicide application cannot be expected to result in a 5-bushel or greater yield increase every year. Spray decisions should be tied closely to disease scouting information. When considering your economic risk, also be aware that foliar fungicides will not protect potential yield components that may be diminished by scab disease (fungus that infects heads at or following flowering), viral diseases (wheat spindle streak mosaic and yellow dwarf), soilborne diseases, or several other environmental factors.

Relative Profit = (Grain Yield Increase x Grain Price) – (Cost of Fungicide + Application Costs)

Spring malting barley
Spring malting barley planted on April 4 in Aurora, NY – photo taken on April 25th (photo by Jaime Cummings, NYS IPM)

Black Cutworm and True Armyworm Monitoring Underway in NY

By Jaime Cummings and Ken Wise of NYS Integrated Pest Management Program

As black cutworm (BCW) moths have been identified in surrounding states, including Pennsylvania and Indiana, this last week in April marks the traditional timing for deployment of pheromone traps in NY to monitor for BCW moths.  Since 2015, the NYS IPM program has coordinated these statewide monitoring efforts in cooperation with numerous Cornell Cooperative Extension (CCE) educators, farmers and crop advisors.  Since BCW is a migratory pest, which arrives on the winds of storms coming up from southern states, knowing when it reaches NY helps us predict when we need to start monitoring for cutting of corn seedlings by BCW caterpillars.  Scouting for significant populations helps farmers make informed management decisions.  Check newly planted fields every few days for signs of missing, cut or wilted plants, and search for the larvae just below the soil surface near damaged plants (Fig. 1).  The economic threshold for BCW treatment is reached when 5% or more plants in the stand have been cut.  The larvae are best controlled when small (< ½”), and soil-applied insecticide rescue treatments at the time of infestation is the most economical and effective management option for BCW infestations.  Lorsban, Pounce and Warrior II all have efficacy against BCW (always consult labels for rates and instructions), and Poncho and Cruiser seed treatments are also labeled for BCW.  Spot treatment is recommended for infested areas of fields, with a 20-40’ surrounding border.  Replant may be necessary if damage is too severe to manage with insecticide.

Black cutworm larva and damage
Figure 1. Black cutworm larva and damage. (Photos courtesy of Ken Wise, NYS IPM)

True armyworms (TAW), another long-ranged migrant from the south, is an inconsistent early-season pest of corn that we are also monitoring for with pheromone traps this spring.  These moths are attracted to weedy or grassy fields, where they will lay their eggs which will hatch and result in numerous larvae moving into crop fields.  Similar to BCW monitoring, the TAW pheromone traps alert us as to the arrival of these moths so that we can predict when we should be scouting for the damaging larvae.  While out scouting for BCW, you should also be on the lookout for TAW damage, which includes ragged holes and leaf margins and abundant pellet-like frass on and around damaged plants (Fig. 2).  The larvae are often found in the whorls or on the soil surface near damaged plants.  The economic threshold for TAW treatment is when >50% of plants show damage and if you count three or more larvae per plant when corn is in whorl stage or younger.  Older corn can tolerate some feeding, and seldom requires treatment.  Lorsban and Pounce have efficacy against TAW (always consult labels for rates and instructions).  Spot treatment is recommended for infested areas of fields, with a 20-40’ surrounding border.

True armyworm damage and larva with frass.
Figure 2. True armyworm damage and larva with frass. (Photos courtesy of Ken Wise, NYS IPM)
Green bucket trap
Figure 3. The green bucket trap with pheromone lure used to monitor pest migration. (Photo courtesy of Ken Wise, NYS IPM)

2019 marks the 5th year of this statewide pheromone trap monitoring network for these pests in NY, and you may see the telltale green bucket traps in your area (Fig. 3).  This year we have 27 traps each for BCW and TAW in 17 counties, broadly covering all field crop production areas of the state.  Financial support for these efforts comes from USDA-NIFA CPPM, and wouldn’t be possible without the dedicated cooperation of many CCE, farmer and crop consultant collaborators.  Monitoring and scouting for pests leads to sound management decisions and the highest economic return on investment for pest management.  For updates on the progress of these monitoring efforts, please subscribe to the NYS IPM Weekly Pest Report.