When Hot Weather Is Real Hot Even for Valley Cotton Plants

As a Central Valley native, you grow accustom to hot summer days and learn to adapt to triple-digit temperatures.  But I must admit the 111-degree weather we had last Saturday (it was just 109 degrees today and last Friday) was a bit excessive even for long-time farmers. It was sooo hot that weather forecasters issued an excessive heat warning over the weekend. I’ll be drinking lots of water this week with triple-digit temperatures expected to last until the weekend.

A cotton plant showing signs of heat stress.
-  Science Daily photo by Stephen Amus 

This heat wave has farmers and others who work outdoors (myself included) getting started really early and heading for cooler environs by mid-afternoon. While hot weather normally provides ideal growing conditions for cotton (the average July and August temperatures around the Valley is the mid- to upper 90s), this excessive heat could turn out to be a little troublesome, especially if these near-record high temperatures last for a spell.

Plants could become stressed; especially for growers who got an early jump on their final crop irrigation of the season. The result could be some bolls opening up early or some fruit dropping – all resulting in a lower yield at harvest time. Check out an interesting article about heat and water stress in cotton by UC cotton expert Bob Hutmacher in the UC Cooperative Extension’s California Cotton Review published in 2004.

Another concern is the super-hot weather could ripen melons or tomatoes faster and prompt farmers to harvest earlier. That could send pests into nearby cotton fields sooner than usual. As Dr. Pete Goodell of UC IPM says, farming is a community as a whole – no matter what crop you grow – and what happens in one field can affect what happens in another. Let’s hope the dominoes don’t start falling. Too bad Mother Nature doesn’t offer air conditioning in the Valley.

Here's the back of a cotton leaf dotted with lots of aphids.

Speaking of pests, we’re almost past the lygus danger zone for cotton. Fields are pretty much at cut-out. But growers still need to monitor for lygus to ensure the smaller bolls at the top of the plant won’t drop. At this time, however, you can allow for a higher pest threshold for possible treatment – five nymphs vs. three for every 50 passes of your sweep net.

I saw aphids on the rise in the past week. But the rate of increase varies from field to field. In general, growers that treated their fields early for the pest or used stronger materials that can impact beneficial insects are experiencing higher counts (a 25 to 40 percent increase) than those farmers who didn’t treat or used softer materials (an 8 to 12 percent increase).  While aphids aren’t a threat right now, we still need to monitor these pests to keep them from becoming a major problem when bolls start to open. That’s when you have to worry about sticky cotton.

A bean plant  habitat next to cotton.

It’s hard to tell when most bolls will start opening. A lot depends on the weather and the timing of the last irrigation.  Conditions are ideal for growers to wrap up or stop irrigating their plants. My guest is we’re around three weeks away for bolls to start opening up.

The alfalfa crop continues to move along without any significant issues. Growers are approaching their fifth cutting. After that they’ll have two or three more before calling it a season in September or October.

On the almond front, our field scout Jenna Horine reports the crop is shaping up nicely with no major pest concerns. Some orchards are experiencing a few more mites than others but there aren’t signs of a potential mite explosion. Dust kicked up from roads around nearby fields remains the major source for mites. Also, the pests are coming from nearby fields where grains and tomatoes are being harvested.

Hullsplit varies. Some nuts are in the early stages of splitting while other nuts are ready to be shaken from the trees. Some growers are still irrigating their orchards while a few already have nuts on the ground. Overall the harvest is following the normal schedule, although growers are saying this is an early season (primarily because the harvest season has been later than usual in recent years).

An almond orchard still getting irrigated.

 Soon, we’ll be collecting nut samples before the crop is sent to the huller. The rule of thumb is to take 500 samples per block and then crack the nuts to check for pests. This practice helps almond growers prepare next year’s management plan as well as helps them compare the grade assigned by the huller. UC IPM has more information online about harvest sampling.