The latest Arizona Vegetable Integrated Pest Management Update from the University of Arizona (UA) Cooperative Extension in Yuma, Ariz. released Oct. 31, 2012.
Aphid identification in leafy vegetables
By John Palumbo, UA research scientist and Extension specialist
This is the time of the growing season when winged (alate) aphids are first observed on desert lettuce and cole crops. The proper identification of winged aphid species found on desert-grown leafy vegetables is important for cost effective pest management.
Most of the important aphid species found on local crops do not over summer here due to high temperatures and the lack of viable hosts. Winged aphids typically begin migration into desert crops in early November; often blown in with gusting winds.
My experience over the past 20 years suggests this is due in part to cooler weather more favorable for the aphid’s behavior and development, plus changes in prevailing winds that now begin to blow into the area from the north and northwest.
Consequently, once the aphids reach the desert valleys, the insects typically move from crop to crop until a suitable host is found to feed and colonize.
It is not uncommon to find winged aphids on lettuce or broccoli which are specific pests of small grains (i.e., corn leaf aphid) or alfalfa (i.e., pea aphid).
Since these aphid species do not colonize lettuce, it is important to distinguish the pest from the key aphid pests commonly found on lettuce which do colonize and require management to prevent problems at harvest (green peach aphid, foxglove aphid, lettuce aphid).
You are likely to find cowpea aphid in lettuce as it is common in alfalfa at this time.
However, experience has shown that although small colonies may be found on lettuce the populations rarely increase in lettuce crops.
The bottom line: proper aphid identification can save a pest control adviser (PCA) time and money, plus prevent unnecessary insecticide applications.
A simple pictorial key provides information that can assist PCAs in the identification of winged aphids important in lettuce and other leafy vegetables.
To view it, click on this link: Aphid ID Key.
Click this link to listen to John's Update.
“Remember, when in doubt - scout.”
Contact Palumbo: (928) 782-3836 or [email protected].
Lettuce wilt disease comparison
By Mike Matheron, UA Extension Plant Pathologist
Fusarium wilt of lettuce, caused by the fungus Fusarium oxysporum, f. sp. lactucae, was first detected on lettuce in Arizona during the 2001-2002 growing season. It is still found in lettuce fields from mid-October through early January.
There is another wilt disease of lettuce called Verticillium wilt caused by the fungus Verticillium dahliae. This disease has occurred in the Salinas Valley since 1995 but has not yet been found in Arizona.
The primary symptoms of each disease are similar - internal discoloration of the root cortex and plant wilting followed by death. The internal root discoloration ranges from green, brown to black in plants infected with Verticillium, and reddish-brown to black in plants infected with Fusarium.
Since symptoms of the wilt diseases are similar, true disease identity can only be achieved by bringing symptomatic lettuce plants to the UA Yuma Agricultural Center in Yuma. The causal pathogen can be isolated from infected root tissue and identified by microscopic examination.
Both wilt pathogens are soil inhabitants which can persist for many years. The pathogens also can be seed-borne.
The lettuce Fusarium pathogen can only infect and cause disease on lettuce, although it may sustain itself on roots of other plants without causing disease symptoms.
Verticillium dahliae, in comparison, can infect and cause disease on numerous crops other than lettuce.
Management strategies for diseases caused by Fusarium oxysporum and Verticillium dahliae are similar.
When available, genetic resistance in host crop plants can provide effective disease control. Soil fumigation and soil solarization can reduce disease levels by lowering viable populations of both pathogens in the soil.
No known fungicides applied after planting have provided consistent and effective control of diseases caused by Fusarium oxysporum or Verticillium dahliae.
Click this link to listen to Mike's Update.
Contact Matheron: (928) 726-6856 or [email protected].
“If you can’t beat ‘em…eat ‘em”
By Barry Tickes, UA Area Agriculture Agent
This is the first in a series which will appear separately in these advisories from time to time which will highlight the nutritional aspects of some common weeds.
The first weed, common purslane, Portulaca oleracea, is one of the most widespread and costly weed problems in this desert region. It is on the Arizona prohibited noxious weeds list.
Common purslane, also called verdolaga, is also a popular and nutritious leafy vegetable. It contains more omega-3 fatty acids than any other leafy vegetable, vitamins A, B, C, plus carotenoids.
Common purslane contains the minerals magnesium, calcium, potassium, and iron. It should not be confused with horse purslane which is in a different family.
There are more than 40 species in the Portulaca or purslane family. Two of these are popular food sources.
Green or common purslane, Portulaca oleracea, is the wild type grown in this area. It grows close to the ground and spreads rapidly.
Golden purslane, Portulaca sativa, grows more upright and has larger leaves. It is cultivated for food. Some think it has better flavor.
Click on this link for recipe and preparation directions provided by Gloria Pena of Yuma, Ariz.
Click this link to listen to Barry's Update.
Contact Tickes: (928) 580-9902 or [email protected].
On another topic, click on this Pigment Inhibitors link to learn how pigment inhibitor herbicides work.