To Scout For Potato Leafhoppers

On June 26, 2019

To Scout For Potato Leafhoppers

Potato leafhoppers have arrived in the state and populations are building in some areas. Extension Entomologist John Tooker explains growers would be wise to keep an eye out for increasing populations of this pest because once their feeding is evident, the economic damage has been done. Potato leafhoppers are perennially the most damaging pest of alfalfa in Pennsylvania, but they can also cause economic damage in other legume forages and some vegetable crops. Their feeding reduces yield and quality (especially lower protein content) and can decrease stand longevity. 

Potato leafhoppers do not live in Pennsylvania all year, but migrate here each spring on storm fronts, arriving in late May and early June. Potato leafhoppers can be frustrating due to the sporadic nature of their infestations—even in bad leafhopper years, many fields escape damage. Once potato leafhoppers colonize alfalfa fields, adults deposit eggs into stems and leaf veins. In warm weather, these eggs will develop into adults in about three weeks, so populations can increase quickly. Potato leafhoppers have straw like mouthparts and extract plant juices. Heavy feeding disrupts nutrient flow within plants, causing yellow triangles to form at the leaflet tips (“hopper burn”), but this evidence of damage does not develop until 7-10 days after feeding begins. As feeding continues, damage gets worse and the chlorotic areas spread toward the base of the leaflet. Once hopper burn is evident, economic loss has occurred.

For non-chemical controls, resistant varieties of alfalfa are valuable. These varieties are covered with fine hairs (the hairs are actually “glandular trichomes”), which decrease leafhopper feeding, but obviously this option needs to be pursued before establishment. Another option is to mix other forages in with alfalfa. Alfalfa/orchardgrass stands (or other combinations) appear much better at tolerating leafhopper damage than pure stands of alfalfa. Spiders and other natural enemies kill potato leafhoppers, so using integrated pest management (IPM) and spraying insecticides only when economically damaging populations develop will help maintain these allies in pest control. In fact, we have growers in Pennsylvania who do not treat their alfalfa fields with insecticides and claim they do not see potato leaf hopper damage; natural enemies would be the best explanation for this lack of damage.

If damaging populations develop, early harvest or insecticides are often the only choices. Early harvest can stop damage, but regrowth should also be scouted to determine if the next cutting also develops damaging populations. To target leafhoppers most effectively, populations should be sampled, and treatment applied only when economic thresholds are exceeded. In Tooker’s experience, regular scouting and use of economic threshold can limit the need for insecticides to once a summer. In most years, it makes the most sense to start sampling in the first week of June and continue to do so periodically. Scouting details and economic thresholds can be found in our Potato Leafhopper Fact Sheet at:

To Consider Alternatives To Corn Silage Where Planting Has Been Delayed

This past year has been one of the wettest on record in many parts of Pennsylvania. As a result, field progress through the fall of 2018 and spring of 2019 have been behind average. With corn planting delayed this spring, you may be wondering if there are options other than corn silage to bale or fill the silo. Extension Agronomists Casey Guindon and Jessica Williamson recommend several options several options for annual forages to take the place of corn silage. 

Forage sorghum is an annual warm-season grass and can be grown and harvested for silage. The feeding value, or Total Digestible Nutrient (TDN) content, of forage sorghum is approximately 85-percent of that of corn silage, with a similar protein content. Forage sorghum makes a relatively similar replacement for corn silage in rations. The optimal planting date is approximately two weeks later than that of corn, and early maturing varieties can be ready to chop for silage in most areas of the state by mid-August. 

When compared to corn silage, production costs per ton of forage sorghum are significantly lower. Forage sorghum can also be advantageous in areas with heavy deer pressure. Studies have shown reduced deer feeding in forage sorghum compared to corn. 

Prussic acid and nitrate accumulation can be problematic in forage sorghum production. However, these compounds are of the most concern when fed to grazing livestock. They are not often an issue when it is harvested for silage, as the harvesting and ensiling processes can reduce the concentration of both compounds in harvested sorghum by as much as 50% after the fermentation processes is complete. 

Sudangrass is another warm-season annual grass that can provide forage in a late planting situation and can be chopped for silage or baled for baleage. According to the Penn State Agronomy Guide, it can be planted as late as July 15th. Sudangrass should be harvested for optimal nutrition at the early head to early bloom stage. Multiple cuttings of Sudangrass may be taken throughout the growing season. Be sure to leave at least 6 inches of stubble at cutting time to improve the speed of regrowth. Prussic acid can also be a concern with Sudangrass but is less problematic in ensiled forages. New varieties produce lower levels of prussic acid than their older counterparts. 

Millets are another annual grass that can provide forage when planted late. Millet is often considered an inferior forage to Sudangrass in terms of nutrient value and yield. However, it may be better suited to cool, poorly drained soils and they also tolerate lower pH soils than other common warm-season annuals.  Along with being adapted to poorly drained soils, millets are also known to be hardy in droughty situations as well.  Like Sudangrass, some varieties of millet regrow after harvest. 

Pearl millet is unique in its characteristic of not having prussic acid accumulation after the first frost of the year.  This forage is ideal for not only harvesting and ensiling, but also grazing because of it’s ability to regrow and it’s absence of the risk of livestock poisoning due to prussic acid toxicity.

Oats are a cool-season annual and can be summer seeded (July-August) for a late fall (October) harvest. Oats have the best quality to yield ratio when harvested at the boot stage and provide a much higher quality diet than warm-season annuals. Another advantage to forage oats is often they only require a 60-day growing window until they can be harvested.

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