Saturday, August 12, 2017

Cotton Aphid Population Explodes Seemingly Out of the Blue in Some Communities

It’s a funny thing about Mother Nature.

One day, everything is going just fine for farmers. A few days later it was another story.

Aphids are showing up in big numbers in some Valley fields.
Cotton field scout Damien Jelen offers a prime example how nature can throw a sudden curveball at farmers. After completing one of his scouting rounds in cotton, Damien noted aphid populations were under control. A few days later, “aphid numbers kind of exploded. They have become a problem,” he says.
The aphid issue appears most prevalent in the Mendota Firebaugh and Kerman areas of the Valley. It’s hard to say why the problem is concentrated in this region.

Experts say the higher populations often surface after heavy watering and fertilizer applications. That may be the case here because the outbreak surfaced a few days after irrigation, Damien says.Certainly, growers are less focused on the why and more focused on the how – like how am I going to stem the infestation. Damien points out the answer has been swift pest treatment. 

Cotton leaf curling is a sign of aphid damage.
Their reasoning: During mid-season, high aphid numbers – more than 50 per leaf – can shrink the size of bolls, stunt plant growth and cause more bolls to be shed from the plant, according to the University of California Integrated Pest Management.

Growers know they have a problem when leaves become cupped or crinkled and experience a build-up of honeydew and sooty mold. In extreme cases, the leaves will start falling off.
The cotton aphid is the most common aphid in California. They can emerge anytime during the season. Here how UC IPM describes the pest: 

Dark colored aphids can reproduce very quickly.
“Cotton aphid is highly variable in body size and color, and adults may be winged or wingless. Nymphs and adults of wingless cotton aphids vary in color from yellow to green to nearly black. The darker forms tend to be substantially larger. Nymphs that are developing into winged adults look very different from the nymphs developing into wingless adults: they bear small welts or protuberances on their bodies and may be covered with a coat of dusty-appearing whitish wax. Their body color is often greenish blue, or amber and blue.”

It’s important to determine the color of the bugs in the field. “The small yellow aphids develop slowly from newborn nymph to adult and do not produce many offspring; thus, their populations rarely increase rapidly. The larger, darker aphids (green and black) are quite different; they develop more rapidly, produce many more offspring in a rapid burst, and can generate rapid population growth rates,” UC IPM says.

The minute pirate bug is a natural enemy to aphids.
 Natural enemies such as minute pirate bugs, bigeyed bugs, green lacewings and damsel bugs can offer some biological control. But UC IPM notes that “although these natural enemies do provide some control, they generally are not able to strongly suppress aphid populations, or cause strong suppression after severe damage has occurred to the plant.”
Meanwhile on the almond front, field scout Jenna Mayfield says pest pressure is down in orchards.
Hulls continue to split and growers are treating for mites on the edge of the orchards where the pest often wind up after migrating from neighboring farms and dusty roads.“I haven’t seen any pest issues,” Jenna says. She also hasn’t seen any shakers rumbling through orchards. “Everyone is waiting to harvest.”
Growers are still waiting to shake their trees.

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