The latest Arizona Vegetable Integrated Pest Management Update from the University of Arizona (UA) Cooperative Extension in Yuma, Ariz. released Sept. 5, 2012.
Whitefly management on fall produce
By John Palumbo, UA Research Scientist and Extension Specialist
Over the last two weeks, whitefly adult numbers on fall melons have been extremely high in trials conducted at the Yuma Agricultural Center. Based on numbers sampled from untreated checks, adult numbers so far have been almost 10 times greater than observed in the past several years.
Furthermore, whitefly pressure has been exceptionally high in the Roll-Tacna areas where our sampling has shown numbers in excess of 150 per leaf on pre-blooming plants in numerous fields.
This high whitefly abundance can be attributed to some extent to the crop landscape in these areas. Crops planted near or adjacent to cotton and alfalfa are clearly more heavily infested.
In addition, our monsoon conditions this year may play a role where total rainfall and average relative humidity during July and August have been higher this year than in the previous 10 years. Interestingly, these monsoon conditions were also very high in 2005 when very heavy whitefly numbers were prevalent.
Since whitefly pressure does not appears to be letting up, pest control advisers (PCA) should pay particular attention to early whitefly control on newly planted produce crops. It is important that PCAs prevent prolonged feeding by high numbers of adults on seedling lettuce plants which can result in stunted growth.
If honeydew is observed on leaves in the absence of nymphs, there are too many adults on the seedling plants.
Furthermore, allowing adults to remain on plants unchecked generally results in the development of large nymph populations which can cause significant growth-yield reductions in all produce crops.
It is strongly recommended that growers apply a soil neonicotinoid on lettuce and cole crops throughout September and early October.
Local research has shown that imidacloprid applied at 0.25 lbs AI/ac (e.g., Alias 2F-16 oz, Wrangler 4F-8 oz; Admire Pro- 7 oz) at planting provides less residual control of nymphs today than 10 to 12 years ago.
Given the current economics of imidacloprid, cost-effective whitefly control can be achieved by using higher rates of imidacloprid to extend residual control ( e.g., Alias-24 oz, Wrangler- 12 oz or Admire Pro- 10.4 oz).
Once plants get larger, products including Movento, Venom, Scorpion, Assail, Knack, and Courier can provide effective nymph control.
With the loss of endosulfan, growers have few options for effective adult control. Good knockdown can be achieved on lettuce and cole crops with combinations of bifenthrin (e.g. Brigade, Sniper, Discipline, etc) or Danitol tank-mixed with Orthene, Lannate, Lorsban, Venom, Scorpion, and Assail.
For more information on whitefly biology, management, and insecticide alternatives, click on this link: Insect Management on Desert Vegetables and Melons: Whiteflies and Whitefly Management in Leafy Vegetables, Cole Crops and Melons
Remember - when in doubt, scout.
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Contact Palumbo: (928) 782-3836 or [email protected].
Soil-borne lettuce pathogens
By Mike Matheron, UA Extension Plant Pathologist
As another lettuce season begins in Arizona so does the threat of diseases caused by soil-borne fungal pathogens. Soil-borne diseases of concern for lettuce now being planted include Fusarium wilt, Sclerotinia drop, and bottom rot.
Symptoms of Fusarium wilt, caused by Fusarium oxysporum f. sp. lactucae can appear on lettuce anytime after thinning. Effective fungicides generally are not available to manage Fusarium wilt, although fumigation with Vapam did provide some disease suppression in an earlier field trial.
This disease is best avoided by not planting susceptible types of lettuce (virtually all head lettuce varieties) in ground known to contain the pathogen, especially during September or October. Soil temperatures during these months favor the growth of Fusarium oxysporum and the resulting development of the wilt disease.
Romaine lettuce cultivars generally are more tolerant to the Fusarium wilt pathogen and can be planted in fields harboring the pathogen in cooler months when the pathogen is less active.
Sclerotinia drop and bottom rot usually do not become apparent in fields until plants are at or past the rosette stage of development.
Successful management of Sclerotinia drop, caused almost exclusively by Sclerotinia minor on lettuce to be harvested in November and December, as well as bottom rot caused by Rhizoctonia solani, require the application of effective fungicides well before the appearance of disease symptoms. Sclerotinia minor and Rhizoctonia solani exist in soil as resistant structures called sclerotia.
Successful management of diseases caused by these pathogens is closely tied to preventing the germination of these sclerotia. Therefore, applications of fungicides are made to the soil where the sclerotia exist.
Early application of fungicides, when plants are very small, facilitates thorough coverage of the bed surface. As plants grow and cover more of the bed surface, fungicide coverage of soil and disease control decline.
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Contact Matheron: (928) 726-6856 or [email protected].
Prowl H20 now registered for Brassica head, stem vegetables
By Barry Tickes, UA Area Agriculture Agent
Brassica head and stem vegetables, including broccoli and cauliflower, have recently been added to the Prowl H20 label. There is no supplemental label. It has been added to the full section 3 Label and use directions can be found there.
It is registered in Arizona but not California.
The label specifies that applications should be made as a directed spray between vegetable rows after the crop has two to four leaves. It can also be applied as a directed spray to transplants that have two to four leaves, one-to-three days after transplanting.
The application rates are from 1.0 pints on course soils up to 2.1 pints on fine textured soil. It cannot be applied within 60 days before broccoli harvest or 70 days before cabbage or other brassica head and stem vegetable harvest.
Prowl H2O is a dinitroanaline herbicide that uses the same mode of action as trifluralin (Teflan), benefin (Balan), and others. Trifluralin is also registered on cole crops and can be applied preplant incorporated.
Other pre-emergence herbicides registered for use on cole crops include Dacthal, Prefar, Devrinol, and oxyflurfen (Goal, Galigan, and others).
Contact Tickes: (928) 580-9902 or [email protected].
The Hercules beetle in Arizona mountains
By Ta-I Huang, UA post doc research associate
The Western hercules beetle, Dynastes grantii, which lives in Arizona pine-pak mixed forests is the largest beetle in the U.S. in terms of body size (2~3 inches) and weight.
Adults have grey background body color with irregular black spots. The immature are typical C-shaped white grubs. Adult beetles feed on tree sap but are not harmful to trees. Larvae feed on decaying wood and soil substrates.
The distribution of this beetle is mainly limited to Arizona (5000~6000 feet elevation), but can also be found in Utah and New Mexico mountain ranges. In some area of Arizona, the Western hercules beetle can be quite common.
We’ve observed 45 adults attracted to the black lights within two hours in the mountains near Payson, Ariz. this summer. Due to nocturnal behavior, this beetle can be found near a porch light, commercial billboard, or in a gas station near the forest.
Another similar species, Dynastes tityus, lives in eastern U.S. and is commonly referred to as the Eastern hercules beetle. The distribution of this species is much more widespread than the Western hercules beetle. It occurs in most of eastern and southern states.
Unlike the pale-grey color of the Western hercules beetle, Eastern hercules beetles have olive green to yellow body color. The biology and ecology are pretty similar for both species.
Hercules beetles are treated as pets in some Asian countries including Japan and Taiwan where they are popular commercial products in the beetle shops because of body size, longevity, and ease in rearing.
The take home message is that these beetles are not agricultural pests, nor pests in forest ecosystems. Chemical sprays for control are unnecessary.
The larvae of hercules beetles are very important and efficient decomposers in our ecosystems which help the process of nutrient recycling.
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For more information, contact Ta-I by e-mail at [email protected].