The latest Arizona Vegetable Integrated Pest Management Update from the University of Arizona (UA) Cooperative Extension in Yuma, Ariz. released May 15, 2013.
Whitefly management on spring melons (part two)
By John Palumbo, UA research scientist and Extension specialist
Over the last week or so, I have received many calls from pest control advisers on which products to use for whitefly adult and nymph control.
I previously discussed whitefly management briefly in the April 17 update but thought it might be good to revisit the discussion since daytime temperatures are in the low 100’s and whitefly populations have reached or are quickly approaching levels which require treatment.
Several factors play a role in determining which insecticide(s) can be applied.
First, population abundance should be a primary factor to determine which product to apply. If nymphs are easily found on crown- and mid-vine leaves, an insect growth regulator (IGR) or IGR-like product is recommended. This includes Vetica, Courier, Oberon, and Knack.
None of these products provide good adult knockdown, but if applied correctly, will eventually suppress adult populations by preventing the development of the nymphal infestation within the field.
The control of adults infesting plants from outside sources requires a different approach. This time last year, I would have recommended endosulfan, but that is no longer an option.
A Vydate+bifenthrin or Danitol tank-mixture is an option, but will likely only provide adult knockdown with limited residual control.
Among the neonicotinoids, Assail and Venom/Scorpion are good options with decent residual control. Since neonicotinoids are used on many crops grown throughout the year, consider the resistance management statements on the label, plus the UA Cross-commodity Guidelines  before application.
This brings up another important factor to consider – the presence of pollinators in the field. Check the label carefully for the environmental hazards statement, specifically for language and restrictions on honey bee safety.
In some cases, products can be used effectively and safely through application timing and rates. In other cases, some products should not be used when pollinators are actively working fields.
Read the label carefully.
The proximity to harvest may limit the choices. The pre-harvest intervals for whitefly products vary from zero to seven days. Also, the presence of worms near harvest may influence the choice of products.
If using a whitefly specific product (e.g., Courier, Oberon, Knack, and Assail), consider adding a pyrethroid for cabbage looper control, or a Lep material (e.g., Intrepid, Coragen, Belt, and Vetica) for the control of both.
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“Remember, when in doubt - scout.”
Contact Palumbo: (928) 782-3836 or [email protected] .
Fusarium wilt on melons
By Mike Matheron, UA Extension Plant Pathologist
A disease which can occur in desert melon production fields is Fusarium wilt.
Symptoms of the disease on melons are similar to Fusarium wilt diseases on other plants, including initial yellowing and wilting on one side of the plant or on one runner, followed by runner collapse. Internal discoloration of the xylem tissue at the base of the plant can be present as well.
As the disease progresses, other runners will show symptoms and collapse, eventually leading to plant death.
Fusarium wilt on cantaloupes and watermelons is caused by two different specific forms of the fungal pathogen Fusarium oxysporum. For cantaloupes and other melons classified as Cucumis melo, the relevant pathogen is Fusarium oxysporum f. sp. melonis. The pathogen for watermelon, Citrullus lanatus), is Fusarium oxysporum f. sp. niveum.
In general, Fusarium wilt severity increases when plants are stressed by temperature extremes, heavy fruit loads, or other plant growth stress factors.
The use of resistant cultivars is a useful disease management tool. However, the performance of a resistant cultivar can be affected by the inoculum level of the pathogen in soil.
According to various published research articles, a rotation out of melons from 3-10 years is needed to significantly reduce but not eliminate the inoculum load of the pathogen in soil.
There are numerous different forms of the Fusarium wilt pathogen. Each form has the capability of initiating disease on one or a few closely related types of plants.
Are you concerned about planting melons in a former lettuce field known to have had Fusarium wilt? No need to worry. The Fusarium wilt pathogen of lettuce (Fusarium oxysporum f. sp. lactucae) will not cause disease on melons.
Click this link to listen to Mike's Update .
Contact Matheron: (928) 726-6856 or [email protected] .
Using fire to control weeds
By Barry Tickes, UA area agriculture agent
This is the time of year when burning fields is widespread and the non-agricultural public is most likely to question this practice.
Controlling weeds is often one of the reasons given for burning. There are probably several good reasons for burning wheat fields but controlling weeds is not one of them.
Burning is a very old agricultural technique. It dates back to prehistoric times and is still used today. It is used in the Yuma area primarily as a post-harvest technique to remove dead or dormant plant material.
It is most common in the summer after grain harvest to facilitate ground preparation for the next crop, or in the spring prior to regrowth of Bermudagrass to remove stubble and stimulate regrowth.
Burning for weed control does not fit well in the Yuma area following wheat harvest for several reasons.
First, wheat is probably one of the most weed-free crops grown here. There are several effective grain herbicides and there is a low tolerance for green weeds in harvested wheat. There just are not that many weeds or weed seeds left to control after harvest.
Second, many studies have been conducted to evaluate burning as a weed control technique. It has been found that summer annual weeds are most affected by burning.
Many of the winter annual weeds in winter vegetables are unaffected since the weeds have a hard seed coat. These include clovers, malva, dodder, sesbania and others.
Burning also has little effect on many perennial weeds, including Bermudagrass, field bindweed, johnsongrass, and nutsedge.
Third, some studies have found that burning is only effective on weed seeds on the soil surface. In one study, about 18 percent of the buried weed seeds were killed. About 90 percent of those on the surface were controlled.
And last, some studies indicate that hot and slow fires are more effective for controlling weed seeds than the flash fires common here when wheat stubble is burned.
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Contact Tickes: (928) 580-9902 or [email protected] .
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