Potato Leafhopper in Alfalfa

Ken Wise and Jaime Cummings NYS IPM

Across the state, there are many reports of potato leafhopper (PLH) approaching threshold in alfalfa. It is important protect your alfalfa quality by knowing what to do and how to determine if a field has a problem.

This insect pest does not over-winter in the Northeast. Adult PLHs migrate on weather from south and south-west part of the county each year.  This year we have had a lot of storms and weather fronts. Many field consultants are reporting finding many numerous adult PLHs in alfalfa fields.

This lime green, slender 1/8 inch long insect can move from plant to plant laying 2-3 eggs per day. Bright yellow-green nymphs hatch from the eggs in search of plant juices.

Potato Leafhopper Adult
Potato Leafhopper Adult
Potato Leafhopper Nymph
Potato Leafhopper Nymph

 

Adults alone seldom reach threshold (and they already have this year), but the combination of the nymphs and the adult can really cause significant damage to the forage. Both the nymphs and adults have piercing-sucking moth parts. As they suck the sugary phloem juices from the plant, they replace it with their toxic saliva.

Large infestations of potato leafhopper in alfalfa can reduce the plant crude protein by 5% and yield by a ½ ton per acre per cutting. If you see V-shaped yellowing on the tips of the leaves you have a good chance that potato leafhopper has been in your alfalfa. This weakens the plant and it will have slower re-growth after harvest and increased chance of winter kill.

V-Shaped Yellowing by Potato Leafhopper
V-Shaped Yellowing
Field Yellowing from Potato Leafhopper
Field Yellowing from Potato Leafhopper

It is TIME TO SCOUT YOUR FIELDS!  Use a 15-inch diameter sweep net to determine if a field is at threshold.

You will want to scout from now until late August. Use the potato leafhopper sequential sampling plan to determine if an infestation requires management or not. The first thing to do is determine the height of your alfalfa. Smaller plants are more vulnerable to potato leafhopper; thus there are different action thresholds for different heights of alfalfa. The second thing you will need to know is how to sample for potato leafhopper.

A sample consists of a set of 10 sweeps of the net. A sweep is one pass in front of you as you walk through the alfalfa. The return swing is counted as another sweep.

Since sequential sampling reduces the number of samples that taken, it reduces the time in each field and tells you whether to treat (management action) or not treat (no management action). Sequential sampling is particularly helpful in minimizing time required to make a management decision in situations where PLH populations are very high or very low. Use the following chart to determine potato leafhopper infestation levels.

Sequential Sampling Card for Potato LeafhopperWrite down the number of potato leafhoppers for each sample taken on the card. Add each sample to the next, keeping a running total of potato leafhoppers. You will need to take at least 3 samples using the sequential sampling method. On the sequential sampling card “N” is defined as no treatment (no management) needed at this time and “T” is defined as treatment (management) needed within in a week. If the sample is smaller than the “N” number stop and scout 7 days later. If the number of leafhoppers is larger than the “T” number then management action needs to be taken within a week. If the number of potato leafhoppers fall between “N” and “T” then continue and take the next sample till a decision can be determined. A guide with a printable version of the sequential sampling chart can be found at: http://www.nysipm.cornell.edu/publications/plh.pdf

Now you need to know what to do if an infestation reaches a management action level. The good news is that you have three good options for controlling an infestation of potato leafhoppers in New York alfalfa.

Option 1: Early Harvest

You can harvest the alfalfa early to control PLH if the field is within a week to ten days of a scheduled harvest. By harvesting the alfalfa early, you’ll prevent potato leafhopper from reaching infestation levels that can cause yield and quality loss to the forage. Make sure that the whole field is harvested at the same time. If a field is not clean harvested then the alfalfa that has not been cut will serve as a refuge for PLH that can re-infest; thus severely damaging alfalfa re-growth.

Option 2: Use an Insecticide

To protect yield and health of new seedings and established alfalfa, insecticide control may be warranted when an infested field is not within a week of harvest. For selection of an insecticide, consult the current issue of Cornell Guide for Integrated Field Crop Management. Remember to read the label and be aware of blooms, bees and the days until harvest restrictions.

Option 3: Plant Potato Leafhopper Resistant Alfalfa

A third option for control is planting PLH-resistant alfalfa. Obviously, it is a little late for this season’s crop but something to consider for future seedings. Research has shown that potato leafhopper resistant alfalfa is consistently higher in quality than susceptible alfalfa varieties with or without potato leafhopper pressure. PLH-resistant variety yields are comparable and generally better than susceptible varieties when PLH are present. A bonus benefit is that currently available alfalfa varieties with PLH resistance have come down in price over the past several years.

PLH DAMAGED ALFALFA NOTE: If you have standing alfalfa with potato leafhopper yellowing across the field, it is best to clip off the alfalfa instead of treating it, and then monitor the regrowth. The reason is that the quality of the PLH damaged forage is going to be poor, at best, and you will get a better quality forage if you protect the regrowth.

For more information check our online IPM video: Time to Scout for Potato Leafhopper in Alfalfa

 

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NNYADP Research Prompts Request for 23 Billion Biocontrol Nematodes by Farmers in Southwest; Protocol Expanding in NY

Cornell University Entomologist Elson Shields, right, talks with farmer Gary Frost as cups filled with biocontrol nematodes from New York State await application on Frost's farm in Dalhart, TX.
Cornell University Entomologist Elson Shields, right, talks with farmer Gary Frost as cups filled with biocontrol nematodes from New York State await application on Frost’s farm in Dalhart, TX. Photo courtesy of Patrick Porter

In May, Cornell University entomologist Elson Shields, Ph.D., and Research Support Specialist Antonio Testa transport 23 billion native New York nematodes to farms in Texas and New Mexico for field application against Western corn rootworm. Shields and Testa, who pioneered the use of biocontrol nematodes as a crop pest management protocol, built a generator-powered system to maintain a temperature of 70 degrees Fahrenheit to protect the nematodes under the cap of a pickup truck.

Researchers, crop consultants, and farmers in several U.S. states are now testing the nematode application, initially developed to beat alfalfa snout beetle back, against an increasing number of agricultural crop pests.

With long-term funding from the farmer-driven Northern New York Agricultural Development Program, Shields and Testa created the science and the nematode-rearing procotol behind the use of native nematodes for controlling alfalfa snout beetle, the most highly destructive crop pest of the alfalfa crops so critical to the regional dairy industry.

Over time, the biocontrol application has been field-tested and increasingly proven its value as a biocontrol for managing pests in corn, berries, potatoes, and potentially other crops.

“The science built and proven in Northern New York over the course of more than 30 years for using the native nematodes as a crop pest biocontrol has steadily expanded to help farmers across New York State and other states and to address pest issues in multiple crops,” said Shields. “The expansion of this cost-effective, easy-to-apply management practice would not be possible were it not for the long-term commitment the farmers of Northern New York needed to develop the science to support a solution for snout beetle.”

With local funding, Texas Agri-Life Extension entomologists and private ag consultants are jointly conducting large farm trials testing the NY nematodes as a biocontrol to manage corn rootworm in Dalhart, TX, and growers have completely funded trials in Riodoso, NM. Applications have been made to more than 900 acres using both ground application and through a center pivot irrigation system.

Having learned of the concept using persistent biocontrol nematodes while working in West Texas, a newly-hired Extension entmologist with Auburn University in Alabama recently contacted Shields about trying the biocontrol nematodes to manage billbugs, a type of beetle that impacts lawn, sod and grass crops.

In 2019 with a new grant from the Northern New York Agricultural Development Program, Cornell University Cooperative Extension Field Crops Specialist Mike Hunter is evaluating the application of the biocontrol nematodes in manure as a way to incorporate the pest management practice into an existing farm task. The research prompted the creation of a new business enterprise now raising the biocontrol nematodes locally for application by farmers and custom spraying services in the Northern New York region.

The number of acres treated with biocontrol nematodes in Northern New York has steadily grown to protect the alfalfa crops on more than 20,000 acres. Shields estimates that recent dairy prices have curbed applications expected to cover more than 100,000 acres with the biocontrol nematodes by this time.

The Shields Lab at Cornell University has also received a Northeast Sustainable Agriculture Research and Education grant to expand biocontrol nematode-corn rootworm applications throughout New York State and to assist similar start-up research in Vermont and Pennsylvania.

Funding for the Northern New York Agricultural Development Program is supported by the New York State Legislature and administered by the New York State Department of Agriculture and Markets.

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Cereal Leaf Beetle Biocontrol Project Underway

Jaime Cummings, Ken Wise and Amara Dunn, NYS IPM

Cereal leaf beetle damage
Cereal leaf beetle damage on the flag leaf of a winter wheat plant. (Photo by J. Cummings, NYS IPM)

The cereal leaf beetle (CLB), Oulema melanopus, can be a significant pest of winter and spring small grains production in NY, especially in parts of western NY.  This invasive species was first detected in Michigan in 1962, and has since become established in many grain producing states in the US, despite quarantine and pesticide eradication efforts in the 1960’s and 1970’s.

Cereal leaf beetle adult and larval stages
Figure 1. Cereal leaf beetle adult and larval stages. (Photos by J. Cummings, NYS IPM)

You may be familiar with this pest either in the larval or beetle stage (Fig. 1).  CLB has one or two generations per growing season, and the adults overwinter in hedgerows, woods or field margins.  We usually start seeing the adults move into small grains fields in April or May to lay eggs which develop into the damaging larvae.  The larger the larvae get, the more damage they inflict on the crop.  After about two weeks of feeding, the larvae drop to the ground and pupate for about two weeks before the adults emerge again.  When looking for these pests, keep an eye out for the typical larval feeding damage that looks like strips of green tissue missing between leaf veins.  Severely damaged leaves may appear skeletonized, and intense feeding pressure in a field may result in a ‘frosted’ appearance of flag leaves (Fig. 2).

Severe cereal leaf beetle larval feeding
Figure 2. Severe cereal leaf beetle larval feeding on winter wheat. (Photo by J. Cummings, NYS IPM)

Considering that the top two leaves of the wheat/barley/oat crop are what contributes most to grain yield, severe infestations of CLB can significantly impact yield and grain quality.  Even in small grain or mixed stand forage crops, this pest can have negative effects on the yield and quality of the forage because they can significantly reduce leaf area and photosynthetic capability of the crop.  It’s important to scout for this pest, usually starting in early to mid-June when larvae are first appearing.  The economic threshold for insecticide application for CLB is when you count an average of three or more larvae per plant before the boot stage or one or more larvae per flag leaf after the boot stage.  Occurrence of this pest can be inconsistent within a field, therefore plan to scout weekly and walk a random pattern throughout each field stopping at 10 random locations to count larvae on 10 plants at each location.  Because insecticides labeled for CLB target the larval stages, in order for your pesticide applications to be most effective, make sure that at least 25% of CLB eggs have hatched and that larvae are present and actively feeding when you decided to spray.  And, if you’re seeing adults in late June or beyond, it’s probably too late to spray for the larvae.  (Always follow label recommendations and restrictions when applying pesticides.)

Paying attention to CLB populations in your fields via scouting is an important part of an integrated management approach for minimizing losses to this pest.  A growing degree day (GDD) model for CLB developed in Michigan determined that adult CLB begin to emerge around 350-400 GDD (base 48) to begin egg laying.  Unfortunately, there is no specific host plant resistance available for CLB, but there are natural predators of the larvae and eggs which can help to keep the pest population in check, and possibly below the economic threshold when well-established in an area.  Lady beetles are known to prey on CLB larvae and eggs, and there is at least one egg parasite though it is not widely distributed.  There is also a CLB larval parasitoid wasp, Tetrastichus julis, which was originally introduced from Europe as a biological control agent in Michigan in 1967 (Fig. 3).  Subsequent releases into other states, including NY in 1973, have led to a sporadic establishment of this biological control parasitoid throughout small grain production areas of the US.

parasitic wasp on a cereal leaf beetle larva
Figure 3. Tetrastichus julis, a parasitic wasp on a cereal leaf beetle larva. (Photo courtesy of Washington State Department of Agriculture)

Given that CLB damage can be widespread and undermanaged in many small grains fields in NYS, and under the advice of Dr. Elson Shields (Cornell University Field Crops Entomologist), the NYS IPM program decided to try to determine the parasitism levels of CLB larvae in various locations around the state and to try to increase populations of the parasitoid in the Aurora area of Cayuga County, where the CLB tends to be a perennial pest.  The multiyear project was initiated this year, with CLB larval collections from locations in six counties.  However, there were no CLB present to collect at two of the locations, so the data collected in 2019 includes only four locations (Table 1).  At each location, a target of approximately 100 CLB larvae of all different sizes/growth stages were collected by hand from wheat, barley or oat fields.  The larvae were temporarily reared in incubation chambers on host plant leaves until approximately half of the larvae were dissected to determine baseline parasitism levels for each location (Fig. 4).  The eggs of the parasitoid are visible when the CLB larvae are cut open under a microscope (Fig. 5).  After baseline parasitism levels were determined for each collection location, the other half of the CLB larvae were then released at the Cornell Musgrave research farm near Aurora, NY (Fig. 6).  This process will be repeated over the next few years.

Cereal leaf beetle rearing chambers and dissection process.
Figure 4. Cereal leaf beetle rearing chambers and dissection process. (Photo by J. Cummings, NYS IPM)
Dissected CLB larvae, and one with T. julis parasitoid eggs
Figure 5. Dissected CLB larvae, and one with T. julis parasitoid eggs. (Photo by J. Cummings, NYS IPM)
Cereal leaf beetle larvae with known level of parasitism being released in Cayuga County
Figure 6. Cereal leaf beetle larvae with known level of parasitism being released in Cayuga County (Photos by J. Thomas-Murphy, Cornell University)

Table 1.  Cereal leaf beetle collection efforts

The goals of this project are to determine the established levels of the T. julis parasitoid around the state since the initial release in 1973, and to try to determine if we can increase its population at the research farm through consecutive releases.  From this first year of data collection, we know that the parasitoid population is low at the research farm (6%) and at two of the collection sites (7% and 10%), but was at approximately 30% at the Ithaca collection site (Fig. 7).  We also know that although there has been a need to spray insecticides to manage CLB at the research farm and near the other collection sites, there has been no need to spray for CLB at the Ithaca collection sites.  It’s likely that the T. julis parasitoid population at the Ithaca site keeps the CLB population below economic threshold levels.  We hope that by intentionally distributing this parasitoid into an area with known CLB problems, we can establish a robust parasitoid population that may result in a reduction of necessary insecticide sprays for this pest.

Figure 7.  Percent T. julis parasitized cereal leaf beetle larvae collected from various locations.
Figure 7. Percent T. julis parasitized cereal leaf beetle larvae collected from various locations.
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