This has been one of the most challenging cotton seasons in recent years for San Joaquin Valley producers because of the late start, and it will not get any easier as growers head into defoliation season.

Last year just about every defoliation treatment worked well, according to Tulare County University of California Cooperative Extension Farm Advisor Steve Wright.

Wright reported on extensive Acala and Pima defoliation trials to those at this season's West Side Research and Extension Center cotton field day at Five Points, Calif.

Product rates will be higher this year to accomplish the same defoliation as last year, said Wright who also expects more pre-treatments to be applied to prepare the crop for defoliation.

Ginstar has become the defoliant of choice because it is effective and does not have the odor of other products and generally gives a defoliation of 75 percent with one application, said Wright.

Last year a 4- to 5-ounce Ginstar rate did an excellent job. This season Wright believes 7 ounces “may be a little bit on the low side as temperatures begin to drop.”

Fortunately the cost of defoliants has dropped as new proprietary and generic materials go on the market. “Treatments that used to cost $40 per acre are now about $30 for a decent defoliation,” he said.

Pima is even tougher to defoliate than Acala in a normal year and this year it will be even more difficult to drop the leaves, said Wright.

“Pima acts like a very aggressive Acala with no boll load,” remarked Wright, who said growers can expect only about 50 percent defoliation with the first treatment, necessitating a second or maybe third application to desiccate and burn remaining leaves.

The sticky lint problem that emerged in the valley has complicated the defoliation and the California Cotton Growers and Ginners Associations along with UC have mounted an aggressive campaign to prevent stickiness after defoliation.

Two weeks or more can elapse between when a defoliant is applied and leaves are all off plants and that is more than enough time for a generation of aphids and whiteflies to develop on the plants and deposit honeydew on the lint, said Wright.

And, very small numbers of insects can do serious damage to lint.

Growers and pest control advisers in several areas of the valley have battled whiteflies all season long. While populations were building early, they crashed. Unfortunately entomologist reported sharp increases in mid-September.

Wright and several other UC researchers conducted defoliation trials lasts season that showed the addition of Orthene and Danitol in defoliants reduced whitefly population. Def and Folex alone also enhanced whitefly control.

“Preferably, whiteflies should be managed before defoliation,” said White. However, they can be managed at defoliation time as well.

e-mail: hcline@primediabusiness.com

Most Effective Acala Defoliations 1995-2000

Defoliation % Cost
Harvade (8 oz) plus Ginstar (6 oz)
B. Sodium Chlorate plus Gramoxone Max (21 oz)
87 $30
Finish (2pt) plus Folex 2 pt 85 $26
Folex (2 pt) plus Prep (2 pt)
B. Sodium Chlorate plus Gramoxone Max (21 oz)
84 $42
Finish (2 pt) plus Ginstar (6 oz) 79 $35
Harvade (8 oz) plus Def (2 pt)
B. Sodium Chlorate plus Gramoxone Max (21 oz)
77 $32
Ginstar (6 oz)
B. Ginstar (8 oz)
76 $25
Folex (2 pt) plus Prep (2pt) plus Agridex (1pt) 74 $30
Ginstar (10 oz) 60 $18
Def (2 pt) plus Accelerate (1 pt) 58 $16
Accelerate (1.5 pt) plus Folex (2 pt) 56 $18
Sodium Chlorate plus Gramoxone Max (11 oz) 55 $23
Def (2 pt) plus Agridex (1 pt) 49 $15
Prep (2 pt)
B. Ginstar (8 oz)
46 $29
(B denotes a follow up defoliation after the initial treatment)