Here’s Some Neighborly Advice on Preventing Unwanted Pest Migration

You might call it flight for survival.

 

We see it around your house after you run into a hornet’s nest, sending the winged pest buzzing away. And we see around orchards after you stomp on an ant hill, sending the bugs skittering about.

That’s what happens when a home is disturbed. Why bring this up? There’s pest management lesson here for growers. And there’s also a reminder here about being a good neighbor

Every season, we point out that pests like their homes, whether it’s a dirt road or an alfalfa field. But when their safe havens get disturbed, they’ll quickly seek a new home.

Take almond orchards. Field scout Carlos Silva has found a small uptick in spider mites in almonds during his weekly monitoring. These pests are found in dry areas, including dirt roads. They can be driven into the trees by trucks kicking up dust on nearby roads.

Keep your speed down when driving on a dirt road.

 Mites will damage foliage by sucking the cell contents from leaves. The leaves then turn yellow and drop, which ultimately reduces the crop and vegetative tree growth the following year.

To help control mites, growers regularly water down roads along the orchard margins to keep dust down. This is where being a good neighbor comes into play: Slow down when driving on roads next to almond orchards. That will be important as the weather heats up, which will make it a challenge to keep dust down.

Lygus bug found in an alfalfa field.

 

The good neighbor policy also applies to alfalfa growers whose crop borders a cotton field. Alfalfa is an ideal host for lygus bugs, which are no threat to the crop. When their home is disturbed, the pests will migrate to a new place, namely cotton. Lygus are a threat to the cotton crop from early squaring through boll set and can cause all sorts of damage – from square dropping to bolls failing to mature. Carlos says lygus numbers have been on the rise in alfalfa recently.



So here’s the hitch: Alfalfa is harvested many times during the season – on average about once of month. That means lygus can be on the move roughly every 30 days.
 Dr. Pete Goodell, a UC IPM advisor and cotton and alfalfa expert, says a good solution to stem the migration of lygus to neighboring cotton fields is to leave uncut strips of alfalfa during harvest. Lygus will travel to these strips and stay there until the next irrigation cycle. The bugs will then go back to the larger alfalfa field as the plants start growing again.

Right now, alfalfa growers have finished their second cutting of the season and have been irrigating the crop. The next harvest should come around the end of May. Goodell tells us that leaving uncut strips is vital from June to July because that time period is a critical stage for cotton development.
UC IPM offers these tips about border-strip strip harvesting: “Leave 10 to 14 foot wide uncut strips adjacent to every other irrigation border (or levee).

Here's an uncut strip of alfalfa next to a cotton field.

“At the subsequent harvest, cut half of the width of the existing 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 percent new) alfalfa making a blend of 25 percent old hay and 75 percent 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 percent new growth alfalfa in most cases.”