|A strip of uncut alfalfa is a good BMP to keep lygus from moving to cotton.|
Monday, June 18, 2012
Cotton Growers Think It's a Cool Time for a Heat Wave
I hope you wore plenty of sun protection because of the furnace-like weather we are having, especially over the weekend. With temperatures hitting triple digits – surging to a record-setting 109 degrees Sunday, breaking the previous high of 107 in 1917 – it must mean one thing: Summer is around the corner – officially Wednesday. But who’s counting with this heat wave.
For our cotton growers, the sizzling triple-digit weather means ideal conditions for faster development of the plants. It also means growers need to remain vigilant about monitoring for pests. So far, I’m finding fields with light lygus counts. On average, I’m collecting about one lygus nymph and no adults during 50 passes of my sweep net. That’s good.
In the meantime, spider mites appear to be under control, thanks in part to the large number of thrips feeding on mite eggs.
With growers finishing up their first irrigation, it is now important to start plant mapping. This will help you track the development of the cotton plants. At the moment, plants are at their 10th and 11th nodes.
This is the time to check for the percentage of fruit retention. Count the top five and bottom five fruiting branches. This lets you know how the plant is doing. As a rule, an 80 percent or higher square retention is ideal going into bloom. UC offers a dandy online calculator to determine the percentage of retention.
If retention drops, growers might opt to use growth regulators to enhance development. But don’t get too excited about getting an early jump on treatment. Check with you pest control advisor, local UC farm advisor or even myself. I’m happy to answer your questions.
Another task for growers is taking the first petiole analysis of the season. You should take the petiole on the third node on the top of the plant. I suggest taking samples from about 40 different locations in the field and then send them to a lab for analysis. The results will show the nitrogen levels in the plant and indicate whether you are using too much or too little fertilizer. The analysis is worth the investment.
At the moment, I haven’t heard about growers treating their fields for mites, aphids or lygus. That’s a good sign. Usually, this is a time for these pests to start building up. If you are going ahead with treatment, make sure you pick softer materials without organophosphate (OPs).
Alfalfa growers are on their third cutting. Some are starting their harvest while others are already baling their hay. Four or five more cuttings are left this season.
I’m seeing lygus counts on the rise in alfalfa. In the past week, the amount of lygus has increased by about 50 percent. We don’t want them reproducing and migrating into nearby cotton fields. It’s really important now for growers to leave more strips of uncut alfalfa. If you have your own sprayer, you might want to consider treating the strips for lygus. Of course, use softer materials that protect the environment and beneficial insects.
The best IPM practice in alfalfa is to leave a strip creating a home for lygus and to keep them from heading into a cotton field. Here’s my suggestion for determining how alfalfa to leave uncut: 1 swath for every 30 to 40 acres of hay grown in the field.
We had a good turnout for last week’s Cotton Field Day. I want to thank Dr. Pete Goodell of UC IPM and UCCE Fresno’s Dan Munk for their presentations. If you missed their talks or want a refresher, the Sustainable Cotton Project has posted them on our website: www.sustainablecotton.org or on YouTube – for Dan’s presentation and Pete’s discussion. There is plenty of useful information. Check them out.