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Areawide Insect Trapping Network

Vegetable IPM Updates Archive

Insect Management

Feb 18, 2015

Corn Earworm in Spring Head lettuce 2015

As the produce season begins to wind down, it would be wise to keep a look out for corn earworm (CEW); they are historically active on spring head lettuce. In the last few years, unusually high CEW abundance has been reported by PCAs on late head lettuce, particularly in the Dome/Wellton areas. Given the CEW trap catches this fall and winter, one might expect to see more CEW than normal, but then again it is impossible to predict. Nonetheless, CEW can be very damaging in spring crops where once head formation begins larvae will usually bore into the head 1-2 days upon hatching. Corn earworm is much more likely to bore into lettuce heads than other Lepidoptera larvae, rendering the heads unmarketable. Larvae may enter the head from any point on the plants, but can often be found burrowing in from the top half of the head. If fields are not watched closely, infestations may not be noticed until the head is harvested. Once inside the head, it is almost impossible to control the larvae with insecticides. Thus, pay careful attention for newly oviposited eggs (laid singly) on lettuce plants. If you are beginning to find eggs and suspect that CEW are active in the field when plants are beginning to head, it would be a good idea to treat. The UA nominal threshold for CEW in head lettuce from early heading to harvest is 1-2 larvae / 100 plants. Repeated insecticide treatments may be required to maintain low population levels near harvest. Most contact insecticides recommended for Lep larvae are active against CEW. Furthermore, the addition of a pyrethroid with thrips, aphid and/or fungicide sprays may be cheap insurance against larvae infesting heads as you approach harvest. For more information on CEW management and control recommendations see Insect Management on Desert Produce: Corn earworm / Tobacco budworm and the 2015 Lep Control Chart.

To contact John Palumbo go to: jpalumbo@ag.Arizona.edu

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Soil Science

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Plant Pathology

Nov 27, 2024

Downy Mildew of Lettuce (2024)

Downy mildew has always been one of the major problem for PCAs and growers in the desert southwest. The symptoms observed are green to yellow angular spots on the upper surface of the leaves and fluffy growth on the lower side (See Picture). Symptoms usually start from older leaves. As disease progresses the lesion turn brown and dry up and in some occasions the disease can become systemic causing dark discoloration of vascular tissue.

Favorable condition for disease development:
The pathogen Bremia lactucae thrives in damp, cool condition, with moisture present on leaves. Spores are short-lived but dispersed efficiently by wind during moist period. Cultivated lettuce is the main host of the pathogen but it has also been reported to infect artichoke, cornflower and strawflower.

Why is downy mildew difficult to manage?
One of the main reason that hinders the disease management is the complexity of the pathogen. Bremia lactucae consists of multiple races (pathotypes), and new races continue to occur as pathogen evolves. The pathogen is one of the fastest evolving plant pathogen. And each pathotypes have developed insensitivity to fungicides to different extent.

One of the best practice is to grow resistant cultivar, but there are limitations. As the pathogen is highly variable and dynamic, resistant cultivars are not a permanent solution as the pathogen overcomes the resistance by evolving into virulent strains and isolates.

Preventative application of fungicides are effective to some extent. Reducing leaf wetness and humidity by using drip or furrow irrigation can be helpful. However, weather condition like rain during cool weather as we had in past couple of weeks is conducive to development of epidemics and we have very little control on that matter.

To contact Bindu Poudel go to: bpoudel@email.arizona.edu

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Mechanization

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Weed Sciences

Oct 12, 2016

Pigweed Control in Lettuce - 2016

Pigweed is a summer annual weed that can persist into the winter and cause problems in early season lettuce. There are 4 species of pigweed here that are all common and widespread. Palmer Ameranth is probably the most common. It is very aggressive and can grow to 6 ft. in height or higher. It has distinctive white veins on the underside of the leaves. This is the one that has become resistant to glyphosate in many agricultural areas including central Arizona. Redroot pigweed is probably the second most common . It is shorter and has stiff spiny scales. The lower stems are often red in reddish Tumble pigweed is much different. It is shorter, grows low to the ground and has smaller leaves. The branches are sticky and break off when mature and tumble in the wind. Prostrate pigweed is similar to tumble pigweed but the leaves are even smaller and create mats on the ground. All of these species need to be controlled before they become well established. Of the three preemergence herbicides registered on lettuce, Prefar is the most effective and Kerb is the least effective on pigweed. Balan is between these two. Cultivation and hand weeding are the only options if these fail. Kerb is the broadest spectrum herbicide on lettuce but this is one broad leave weed that can be more effectively controlled with Prefar and Balan.

To contact Marco Pena go to: marcop@ag.arizona.edu

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Specialty Crops

Organic Crops

Areawide Insect Trapping Network

Jan 8, 2025

Area wide Insect Trapping Network (January 8, 2025)

Results of pheromone and sticky trap catches can be viewed here.

Corn earworm: CEW moth counts down in all traps over the last month; about average for December.

Beet armyworm: Moth trap counts decreased in all areas in the last 2 weeks but appear to remain active in some areas, and average for this time of the year.

Cabbage looper: Moths increased in the past 2 weeks, and average for this time of the season.

Diamondback moth: Adults increased in several locations last, particularly in the Yuma Valley most traps. Below average for December.

Whitefly: Adult movement remains low in all areas, consistent with previous years

Thrips: Thrips adult movement continues to decline, overall activity below average for December.

Aphids: Winged aphids still actively moving but declined movement in the last 2 weeks. About average for December.

Leafminers: Adult activity down in most locations, below average for this time of season.

To contact John Palumbo go to: jpalumbo@ag.arizona.edu

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Vegetable IPM Updates Archive

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