Pearl Snaps

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Forage Facts: Potato Leafhoppers

Potato leafhopper (Empoasca fabae) is a major pest of alfalfa and other legume forage crops.  In Pennsylvania, it causes over $15 million in average losses annually.  It reduces yields, quality (especially lower protein content), and stand longevity. The stress leafhoppers trigger has increased root rot and stand failures. This damage is especially evident in new seedings.

Leafhopper nymphs and adults feed on the undersides of the leaves.  By extracting the sap, they cause stunting and leaf curl, as well as a yellowing of leaf tissue known as “hopper burn.”  This discoloration is caused by injection of a toxic substance into the leaf tissue.  “Hopper burn” is characterized by a yellowing of the tissue at the tip and around the leaf margin which continues to increase until the leaf dies.  Many times this can be confused with drought stress.

Leafhoppers overwinter in the southern Gulf states and migrate north in the spring.  After mating, eggs are laid inside the veins on the underside of leaves. A female leafhopper lives about a month, producing only 6 eggs a day.  Eggs hatch in about 10 days, nymphs mature in about 2 weeks, and begin feeding on leaf tissue.  Mating occurs about 48 hours after maturation.  As many as 3-4 generations can be produced in one year.

For more information on when and how to sample your forage stand for potato leafhoppers and how to determine your economic injury threshold, visit Penn State’s Entomology website.

Options for control of potato leafhopper available in today’s market are insecticides and recently, new varieties of leafhopper-resistant alfalfa. To read more about chemical control options, you can consult this University of Delware publication or the Penn State Agronomy Guide.


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Forage Facts: Alfalfa Weevil

Alfalfa weevil (Hypera postica) can be a major problem insect in the first cutting of alfalfa.  This insect is one of the primary defoliators of alfalfa.  The alfalfa weevil was introduced into the United States from southern Europe and was first found in 1904 in Utah.  It can be found in all 48 mainland states today.  Alfalfa weevil along with it’s other insect counterpart, the potato leafhopper, are responsible for hundereds of millions of dollars in losses annually for farmers.  It is estimated that a 10-15% reduction in yield alone (not considering forage quality) can be seen from alfalfa weevil damage.

Adult weevils lay eggs in the stems and stubble of alfalfa plants in the Fall.  The eggs overwinter and hatch in early spring.  Spring laid eggs hatch immediately.  The larvae stage lasts approximately 3 weeks followed by the spinning of a cocoon.  The larvae remains in the cocoon for about 10 days and upon emergence is a fully mature adult weevil.  During mid-summer adults become inactive.

The larvae feed within the growing tips of the alfalfa plant, on the upper leaves as they emerge, and later on lower leaves.  Eventually plants become skeletonized from feeding and leaves die, giving the field a frosted appearance.  Larvae may also feed on new emerging shoots and can severely inhibit regrowth after cutting.  Adult weevils feed on the entire alfalfa plant.  Conditions that favor pest development are excessive pesticide use (which destroys biological control agents), mild winters, and warm dry spring weather.

Methods to control alfalfa weevil include management practices, biological agents, and pesticides.  Management practices that maximize alfalfa growth will minimize the effect of alfalfa weevils.  Several species of parasitic wasp and a fungus exist that will help control alfalfa weevil populations biologically.  If infestation levels are above the economic threshold, pesticides must be used, but always remember that insecticides kill beneficial insects too!

To sample for alfalfa weevil in your stand you can take the following steps:

  1. Collect 30-50 stems randomly from throughout the field.
  2. Shake larvae out of stems. Open young leaves to dislodge young larvae.
  3. Count larvae.
  4. Determine average length of stems.
  5. Use charts below to determine if control is warranted.

via Penn State Entomology

For more in-depth descriptions of life cycle, crop injury, crop scouting techniques, and crop management please consult the following links:


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Forage Facts: Weed Control in Forages

by Jesse Bussard

Weeds can be a pose a major problem for many forage producers.  Weeds can negatively impact forage yield, stand persistence, and forage quality.  Forage yield is effected because weeds will ultimately contribute to the total yield of the forage crop and can drastically reduce the total amount of desired forage in the hay crop.

Once established forages can out compete most weeds.  The exception would be aggressive winter annual weeds such as chickweed.  If a forage stand becomes invaded with weeds, the stand’s persistence will weaken.  This can be caused by a number of factors including diseases, insects, low fertility, winter damage, and improper cutting management.

The largest affect weeds have on a forage crop is by reducing forage quality.  Contrary to what you may think though, weeds are not necessarily always low in quality.  Weeds such as barnyardgrass or giant foxtail are actually quite nutritious.

So if there are weeds high in quality, then why do we associate them with low forage quality?  The reason lies in the fact that most forage quality tests do not include a palatability measurement.  The crude protein content means nothing if animals won’t eat it.  Another issue with weeds in forages include the fact that many weeds dry slower, which delays baling and increases exposure of forages.  Weeds also tend to generally mature earlier than forage species.

When planting a new forage crop, the most critical weed control period is the first 60 days of forage emergence.  Weeds that emerge along with the forage crop are generally the biggest issue.

To control or not to control?  That’s the big question.  When considering what weed control tactics to use it’s important to ask yourself the following questions:

  • What is the intended use of the forage
    • On farm use can generally tolerate some weeds.
    • Forage to be marketed can not tolerate weeds.
  • How old is the forage stand?
    • Young stands (<2 yrs) can compensate and fill in better than old stands.
    • Older forage stands (>4 yrs) may not compensate for yield loss when weeds are eliminated.
  • How think is the forage stand?
    • Non-spreading forage species (no rhizomes or stolons) have a stand density threshold below which production is not economical (alfalfa is 4-5 plants/sq ft).
  • What is the weed species and how bad is the infestation?
    • What is weed quality relative to time of harvest?
    • Is it a noxious or poisonous weed?

There are many methods to control weeds in your forage crops.  When establishing a new forage seeding it is important to buy certified (weed-free) seed.  Be sure to control weeds in the proceeding crop.  Another thing that isn’t always considered is animal manure.  Feeding weed seeds to animals does not always kill the seeds.  Many times manure is contaminated with weed seeds, so care must be taken to not spread manure that is loaded with weed seeds on a new seeding field.

To ensure a good stand it is important to maximize the competitive edge of forages.  This can be done by selecting adaptable species and varieties and in return this reduces chances of diseases, insects, and winter damage.  It is essential to also provide the optimum growing environment for forage growth with and ideal pH, soil fertility, and proper cutting management.

It is also important to minimize the competitive ability of your weeds.  Depleting root carbohydrates by cutting them before they are mature, before seed production, through practices such as mowing will decrease weed competitiveness.  A note for producers applying manure, adding manure to pure legume stands will encourage grass weed invasion.

In the end if a weed problem is still present, herbicides can be used.  There are many herbicides available that will control broadleaf weeds in grasses and also grass/broadleaf control in legume forages.  Unfortunately very little if any herbicides exist that offer control weeds in legume-grass mixtures or for grass weeds in forage grass crops.

For more information about weed control in forages, follow the links below to these extension publications:

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