Monday, June 6, 2016

How to Be a Good Neighbor: Strip-cut Your Alfalfa Fields



While making his rounds around the Valley last week, field scout Carlos Silva noticed a grower had just harvested his field of golden brown alfalfa.

The freshly-cut alfalfa lay drying on the sun-baked field, waiting to be collected and formed into bales. Nothing usual about that sight. Still, one thing stood out: “There were no strips of uncut alfalfa in the field,” Carlos says. It was surprising because a cotton field was right next door.

There are lots of lygus bugs living in alfalfa fields right now.
You might ask why this is a surprise. Well, lygus bugs are plentiful in alfalfa right now and this pest is a threat to cotton, especially now that the plants are developing their early squares – the flower buds of the cotton plant.

Around the Valley, you’ll often find cotton and alfalfa planted in neighboring fields. Lygus bugs prefer alfalfa over cotton as a home. But when their habitat is disturbed every month or so when alfalfa is harvested, the bugs literally bug out and set down in the cotton fields.

Already, Carlos is discovering lygus bugs in some cotton fields. His sweep net is gathering one to three bugs for every 50 sweeps. Lygus will be a big worry for cotton growers until final boll set later this summer.

Here is an example of a cotton square with lygus bug damage.
Here’s what UC Integrated Pest Management says about the destruction the pest can have on cotton: “Lygus bugs pierce squares and damage anthers and other tissues. When squares are less than 0.2 inch (5 mm) long, they shrivel, turn brown, and drop from the plant. Damage to larger squares may be to anthers, styles, and stigma, and may interfere with fertilization. If many squares drop, the plant may put its energy resources into vegetative growth, resulting in tall, spindly plants and reduced yields. Lygus bugs also feed on and destroy terminal meristems, causing bushy plants. If these bugs pierce the wall of young bolls (typically less than 10 days old) and feed on young seeds, these seeds may fail to develop. Lint around the injured seeds is stained yellow and may not mature normally.”

Carlos reports some instances of squares falling off. It’s unclear if the drop is due to lygus bug damage or other stress. One thing is for certain, cotton growers have a near zero tolerance for the pest. UC IPM suggests treatment until mid-June at one bug per 50 sweeps of the sweep net and two bugs per 50 through the end of this month. Spraying, however, can be harmful to beneficial insects. That’s why cultural controls are preferred pest management strategy at the outset.

So here we come full circle to back to alfalfa fields and leaving a habitat for lygus and reducing the migration to cotton. Here are strip-cutting tips from UC IPM:

·         Leave 10 to 14 foot wide uncut strip adjacent to every other irrigation border (or levee). At the subsequent harvest, these strips are cut with half of the alfalfa strip going into one windrow and the other half going into a second windrow to give a 50:50 blend of new and old hay. These windrows are then each combined with a windrow of newly cut (100% new) alfalfa making a blend of 25% old hay and 75% new hay. This technique minimizes quality problems from the older hay. Specific blends of old and new hay have been found not to significantly impact forage quality compared to 100% new growth alfalfa in most cases.
·          At the following cutting, uncut strips are left adjacent to the alternate irrigation borders. As an alternative, uncut strips of alfalfa may be left adjacent to the crop to be protected, such as cotton or dry beans. 
A grower leaves a strip of uncut alfalfa near a field of cotton.
 Carlos says this practice should be followed for alfalfa fields that are within a two mile radius of a cotton field. Lygus bugs can easily travel that far after their habitat is disrupted.Carlos will be reminding growers that strip cutting is the neighborly thing to do.

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