Cotton growers are becoming more creative in treating for whitefly, now that they have a much broader selection of controls.
In California, some growers are getting by with a single treatment by combining an insect growth regulator (IGR) with endosulfan, or other adulticide. But in Arizona, where whitefly pressure is so high, that’s usually not possible, so growers are using an IGR as their first and second lines of defense.
Admire and the other neonicotinoids are as effective as always, but are usually reserved for aphids and lygus earlier in the season in California, or for neighboring crops in both California and Arizona. And Oberon is now available as a selective first line of defense, especially if mites are present.
Matthew Phillips, an independent Professional Crop Advisor (PCA) in Yuma, AZ, uses a systematic approach for scouting, saying, “We started watching our fields in mid-April, and can start spraying as early as mid-June. We watch the nymph population. If it’s building slowly, we will treat with an IGR – usually Courier, but we also use Knack occasionally. If we have really high adult populations coming in fast – say, tripling in a week’s time – we will throw some endosulfan in the tank.
“The endosulfan takes care of the adults and the IGR gives us a good 30-40 days of control, and can usually carry us through the season,” he continues. “Occasionally, we will have to make a second spray with an IGR, and we will rotate to a different IGR for that late spray.”
He will consider Intruder (a neonicotinoid), but to avoid potential resistance problems, he prefers not to use it in cotton because melons, that can be in nearby fields, are already treated with Admire. He will add Oberon if mites are present, or simply to rotate to a different IGR.
Mike Mullion, a grower and PCA in Blythe, CA, takes a similar approach, except he usually uses Knack in his first IGR treatment and Courier in his second. “We’re in the desert, right on the Arizona/California border,” he says. “With the crop rotations we have, our cotton is surrounded by alfalfa and melons, so we get some pretty high whitefly populations. I like Knack in my first application because it’s translaminar (systemic).” But, he says, later in the season when the leaf hardens and won’t absorb Knack, he switches to Courier.
Mullion says mites occasionally invade his fields from nearby alfalfa fields, “so I use Oberon on maybe 20% of my acres.”
Probably the most innovative idea is coming from California’s San Joaquin Valley, where lighter whitefly pressure is allowing growers to get by with a single treatment of Courier and an adulticide. “I wait until I have 5-7 adults on the fifth leaf; there’s usually 1-5 nymphs per leaf at that time, too,” says Matt Chase, a PCA with Helena Chemical in Hanford. “Then, I come in with Courier and endosulfan — either Thionex or Thiodan. Or if I can’t use endosulfan because of restrictions, I’ll use a combination of a pyrethroid, like Mustang or Warrior, along with an organophosphate like Lorsban. I sometimes use Assail as my adulticide. It isn’t a true knockdown, but it does a pretty good job, plus it picks up aphids,” says Chase.
The adulticide knocks out any adults in the field, explains Chase, while the IGR stops nymphs from developing into adults, giving him a month or more of residual. Courier and Knack are the two IGRs registered for cotton, but Knack needs to be applied earlier in the season to be effective, he says. “That’s what I like about Courier – you can apply it early or late,” says Chase.