Dormant alfalfa shows tire track damage in Willow Street, Pa.

Now is the time to walk and evaluate your alfalfa fields.

Survival and high production of an alfalfa stand begin with an understanding of root reserves.

Alfalfa is a perennial forage crop. Its leaves use sunlight to produce sugars and starches; these carbohydrates are used to support growth.

When levels of carbohydrates exceed the need for regrowth, the excess amounts are transported to the tap root and stored for future regrowth. This regrowth may come between cuttings or at spring greenup.

During winter, alfalfa plants are in “hibernation,” but they still carry on basic plant functions requiring stored carbohydrates. Management that maximizes root reserves at the onset of cool temperatures and short days in the fall sets the stage for optimizing alfalfa stand survival in the spring.

Winter survivability is influenced by many factors:

Stand Age: Younger stands are more stress tolerant than older ones. Younger stands have lower levels of disease incidence and less physical damage.

Soil Fertility: Stands with high levels of potassium are less likely to experience winter injury than stands grown on low fertility. Potassium is vital for carbohydrate movement to the tap root. Soil pH above 6.5 is also preferred.

Soil Moisture: Most winter injury is actually caused by the plant drying out. High soil moisture increases freezing and thawing cycles, which “heave” the crowns out of the soil. This heaving tears roots off and exposes the crown to cold, drying winds.

Cutting Management: The shorter the interval between cuttings during the growing season, the greater the risk of winter injury.

Allow plants to reach 10% bloom between at least one cutting. Also, attempt to time the last cutting several weeks prior to a killing frost, or take a high cutting after a killing frost and the plants have become dormant.

Fields that go into the winter with low root reserves will be particularly susceptible to winter injury and winter kill and will also come back slowly and unevenly in the spring.

Now is the time to not only check your fields for weed pressure, but to determine the extent of winter injury.

Fields that have significant weed pressure and reduced populations of desirable alfalfa and grasses should be considered for rotation to corn or another crop.

If stands are uneven, many growers will take a first cutting and then plant corn for silage. This practice is a great way to utilize the extra nitrogen. Also, many herbicide options can be used in corn fields to terminate alfalfa regrowth.

Look over the entire stand to get a feeling of uniformity or unevenness, then look closely at several sites in each field. Observe buds, shoots, crowns and roots. Look for bright green shoots, healthy buds and firm white roots. Check stands more than once, as some fields may develop more slowly than others.

Stem counts are used to evaluate the yield potential of pure alfalfa stands.

Make a frame of wire 1 foot square, toss the frame into a representative area, and then count the number of stems within the frame.

Fields averaging more than 55 stems per square foot will have the highest yield potential. Stands between 40 to 55 stems per square foot will have some yield loss, and stands with less than 40 stems per square foot should be considered for rotation.

Now is the time to consider weather and other effects on insect pests of field crops.

Delbert Voight, a Penn State agronomy educator in Lebanon County, reminds us that many pests can be affected by winter conditions.

A large amount of insect mortality occurs in winter. Insects perish due to cold temperatures and diseases that attack them while they are in the resting stage.

Grubs, for example, overwinter as larvae, and many are killed by a pathogen that infects their outer skin, which desiccates (dries out) the body.

Some insects, which normally overwinter in surface residue (leaves, corn stalks, etc.) or soil don’t burrow deep enough in the soil to survive winter and can be killed by cold temperatures.

This winter was relatively mild early on, which may cause an increase in the number of insects that overwinter and may bring increased insect pressure this coming season.

On the other hand, if the mild weather prompted some insects to start growth, they may have perished in the cold month of February.

Many factors come into play, and thus it is difficult to make a prediction. For example, snow insulates the soil and lessens the mortality of insects.

Insect hatches usually occur when the host (preferred food of the insect) is present. If the host is not present in sufficient quantity to support the insects when they hatch, the insects will die.

This is why crop rotation is critical. By rotating the crop (corn, soybean), the insect life cycle is broken and the insect population plummets.

For example, the most effective rootworm (common insect pest in corn) control in corn is to rotate to soybeans to break the life cycle.

Another method, effective on black cutworm, is to delay planting for 12 days after burndown of fields infested with chickweed and other spring weeds.

This makes the field unattractive to the moths migrating north and allows freshly hatched worms to starve before corn emergence.

Insects such as corn rootworms and grubs lay eggs in late summer. Soil and weather (moisture) conditions from August through April will affect survival of their eggs and larvae.

At this point, it is difficult to tell which insect species, if any, are going to be a significant problem in 2021.

One can bet that some random fields will have significant pest pressure; however, this could be for reasons other than weather, such as rotation and tillage system impacts.

It is wise to begin planning now to manage these pests. Learn to identify and scout for the most common insect pests of field crops in your location.

Seed treatments, in combination with postemergence applications of pyrethroids, may prove useful in managing these pests; however, by understanding the behavior and requirements of pests more effectively, pest management programs may be developed to lessen our reliance on pesticides and ensure adequate control of pests.

When you or your crop scout does this, you are practicing integrated pest management. IPM is a practice that requires some attention to detail but can have significant rewards for your pocket and for your community.

If you have an unknown insect, disease or weed or just want more information about a particular pest, visit or call your local Extension office.

Jeff Graybill is a Penn State Extension agronomy educator in Lancaster County.

Jeff Graybill is a Penn State Extension agronomy educator in Lancaster County.


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