Monday, June 4, 2012

Cotton Plants Getting Ready for the First Irrigation of Season

As we say hello to June and good-by to May, we can certainly look back at a month of near record temperatures – both on the minimum and maximum sides. These yo-yo temperatures played roles in early season decisions for growers of all crops.

First, let me put my weather hat on and review the historical climatological data for the Fresno region from the National Weather Service. Normally, our temperatures average in the 80s (see chart below), steadily rising as we head toward Memorial Day.

As you can see in the temperature chart I put together, May 2012 (the top darker green line) certainly had its ups and downs, including the last week of the month. On May 9, the thermometer officially hit 98 degrees (probably in the 100s in some hot spots), coming close to all-time record high of 101 on that date, which was recorded in 2001.

Then on May 25, Mother Nature caught a cold and sent temperatures plummeting to reach a high of only 69 degrees, close to the all-time minimum high temperature of 68 reached back in 1890. The weather slowly warmed up in the past week, hitting a torching 104 last Friday – the first day of June.

For cotton growers, who have finished applying fertilizer to their crop, it might be wise to put off their first irrigation of the season until at least Tuesday. Because of crazy temperature swings, the number of heat units hasn’t reached a high enough threshold to make it ideal to start irrigating the cotton.

The timing of the first irrigation could make the difference of a yield increase of 400 pounds of cotton lint per acre, according to University of California researchers. (UCCE pdf) Air temperature changes, drying winds, rainfall since pre-irrigation before planting and rooting volume due to diseases and soil conditions are factors in scheduling the first irrigation.

Here's an example of a pinhead square.
You want to make the young cotton plants a little thirsty and cause a little stress, pushing the pinhead squares to develop on sixth or seventh node. This way, you will get more fruiting branches. If growers irrigate too early, that can stimulate vegetative growth in the plant. Then they might have to spend money on plant growth regulators. For now, I’m seeing growers preparing ditches and laying out pipes, but not yet starting the water.

On the insect front, some fields are experiencing light damage from thrips. But I expect plants to recover from any damage, so there’s a good chance growers won’t have to treat for this pest. On the plus side, the thrips are feeding on the spider mite eggs, which should keep the mite population down. I’m spotting a few more mites in some fields. I suspect that’s due to the relatively dry winter we experienced in the Valley.

Meanwhile, the early review on the alfalfa crop is the yields are looking good. There haven’t been any major pest threats so far. Still I suggest growers keep monitoring for worms.

Save the Date: Remember to put June 12 on your calendar for our Cotton Field Day. We will feature UC IPM advisor Dr. Pete Goodell and UCCE Fresno County cotton specialist Dan Munk. They will offer valuable tips for early season pest and agronomic management during the 10 a.m. to noon event at the Housley and Vandenberg Farm on Sierra Avenue in Firebaugh. Directions are available in the events section of the Sustainable Cotton Project’s website –  One and a half hours of continuing education credits have been approved. Bring your questions.

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