Monday, June 11, 2012

X Marks the Spot for Sweeping Your Fields to Monitor Pests


Cotton growers are finishing the first crop irrigation.

Cotton season is in full swing with growers now wrapping up the first irrigation. The watering, mixed in with fertilizer folded into the soil earlier, are now combining to help these plants thrive and develop lots of fruit.

I’m spotting the first pinhead squares at the fifth to sixth node. That’s a good sign because normally you find the first pinheads developing at the sixth to seventh nodes. This means the plants could develop more fiber-bearing fruit, likely translating into a higher yield at harvest time.

At this plant development stage, growers now need to be more vigilant about monitoring for pests, especially lygus, the bane of all cotton growers. Lygus can damage squares at all stages of development. It’s important to monitor for this pest to keep the first crop.
Lygus can be trouble.
- UC IPM photo

In this high-tech age, the most effective way to monitor for lygus is the old-fashion way – using a sweep net.
 Here’s the field scout’s short course on sweep net sampling: Pick three or four different locations of the cotton field to perform the sweeps. Picture a big “X” overlaid on top of your field and take your pest samples at each leg of the X. This ensures your locations are equally spaces out to give you a good overview or sample from your entire acreage. You also can follow a “V” pattern. 

 Net sampling should be done weekly. Also be sure to rotate the sample locations to ensure you cover all areas of the field.

The technique is pretty straight forward. As you walk down a row, you move in a sweeping motion back and forth or right to left (left to right if you’re a lefty). Image the sweep net as a tennis racket. One sweep is a forehand move and the second sweep is a backhand motion – Spanish tennis superstar Rafael Nadal would be proud. In each location, you want to do 50 sweeps.

Check the UC IPM online for lygus monitoring for cotton for more information about sweep net sampling and pesticide treatment thresholds. I can’t stress it enough, now this is the time to be vigilant about regular pest monitoring in the field. Spending time and labor on this task, saves time and money in the long run by reducing chemical inputs and costs as well as increasing yields.

It's important to monitor
for pests with a sweep net.
- UC IPM photo
This also is the time to do plant mapping. While I tell growers a plant can hold only so much fruit, the idea is to achieve the ideal maximum amount of fruit. Mapping isn’t an exercise in cartography – the art of making maps. The real world application is simple: Mapping lets you track the plant’s growth and development throughout the season and plays an important role in treatment and management decisions. Again, here’s a UC link to learn more about cotton plant mapping.

Right now, some growers may want to use growth regulators to slow vegetative growth and set more fruit. However, I suggest growers not jump the gun on this. With the first irrigation taking place and fertilizer already feeding the plants, cotton plants are getting food to grow. Applying growth regulators at this same time would seem counterproductive.

This also is a good time to take plant tissue samples. By analyzing the tissue, you can get a read on the level of nitrogen, or fertilizer, in the plant and decide if the plant is getting too much nutrients or not enough. I’ll speak more on this topic in my next blog.

Fusarium wilt is more evident in fields.
On the plant disease front, I am seeing quite a bit of evidence of fusarium wilt damage. It’s the most I’ve seen in the past couple of years. Weather may be a factor causing this problem. I would check in with Fresno County’s UC Cooperative Extension cotton specialist Dan Munk about any concerns in your field.

Looking at alfalfa, growers are finished with the second cutting and now moving onto irrigating again and applying nitrogen to feed their crop. I’m spotting a light amount of worms and an uptick in lygus.

So far, growers are doing a good job of leaving uncut strips of alfalfa to prevent lygus from migrating to nearby cotton fields. It hasn’t reached the point yet where growers need to treat their alfalfa. Natural predators seem to be keeping crop-damaging pests in check at the moment. Again pest monitoring remains important here as well.


Cotton Field Day: Remember Tuesday’s event (June 12) will be from 10 a.m. to noon at the Housley and Vandenberg Farm on Sierra Avenue in Firebaugh. We will feature UC IPM advisor Dr. Pete Goodell and farm advisor Dan Munk. They will offer valuable tips for early season pest and agronomic management.  Directions are available in the events section of the Sustainable Cotton Project’s website – www.sustainablecotton.org.  One and a half hours of continuing education credits have been approved. It will be worth your time to get your questions answered directly from these UC experts. I will see you there.


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