Arizona Veg IPM Update: IRM guidelines, powdery mildew, lettuce injury

Arizona Veg IPM Update: IRM guidelines, powdery mildew, lettuce injury

The latest news on IRM guidelines, powdery mildew, and lettuce injury from University of Arizona specialists in Yuma, County, Ariz. 

The Arizona Vegetable Integrated Pest Management Update from the University of Arizona (UA) Cooperative Extension in Yuma, Ariz. released Oct. 2, 2013.

IRM guidelines for Lepidopterous larvae in lettuce

By John Palumbo, UA research scientist and Extension specialist

Lepidopterous larvae, including beet armyworm, cabbage looper, and corn earworm, are major pests of leafy vegetables grown in the Desert Southwest.

Typically, larval populations begin infesting newly planted produce stands soon after plants emerge in early September and can remain heavy through early November under favorable weather conditions.

This year is no different. Populations are heavy in spots throughout the area. Fortunately for local pest control advisers (PCAs), several insecticide alternatives are available which provide excellent residual activity on this pest.

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Many of the products have different modes of action (MOA) that can be alternated throughout the growing season. The rapid development of resistance by lepidopterous larvae, and in particular beet armyworm, to any of these insecticide compounds should not readily occur.

However, if an insecticide compound, or products with the same MOA, are used repeatedly for Lep control in the same field, the risk of resistance increases significantly.

This is particularly important with the Diamide group of insecticides (IRAC group 28) since  these products can be applied as foliar sprays and soil injections, and since there are currently six Diamide products labeled in leafy vegetables with the same MOA (Coragen, Durivo, Voliam Xpress, Voliam Flexi, Belt, and Vetica).

Applying these Diamide products to the soil at planting and applying the products as foliar sprays in the same field can expose multiple generations of Lep larvae to the same MOA. That is not a good way to use these products for effectiveness for more than a couple of years.

Since the Diamides, plus other products currently available (Radiant, Proclaim, Intrepid, Avaunt), are critical to effective management of Lep larvae in leafy vegetables, PCAs should consciously avoid the overuse of any of these compounds.

The most effective way to delay the onset of resistance by BAW in leafy vegetables is to consider the recommendations provided in the guidelines recently prepared entitled Insecticide Resistance Management Guidelines for Beet Armyworm in Lettuce [5].

Listen to John's Update [6]

“Remember, when in doubt - scout.”

Contact Palumbo: (928) 782-3836 or [email protected] [7].

Powdery mildew on fall melons

By Mike Matheron, UA Extension Plant Pathologist

Along with concerns for virus and other pest problems, melon growers should remember that powdery mildew can occur on fall plantings.

Similar to disease development in the spring and summer, powdery mildew first becomes apparent as very small colonies which may at first be few in number. However, these spots will enlarge and produce ever larger quantities of spores which in turn initiate more infections and increase powdery mildew coverage of melon leaves.

Compared to powdery mildew in the spring and summer, the rate of disease development may be slower on fall melons due to lower temperatures as plants progress to maturity.

Past fungicide evaluation trials showed that several registered fungicides can provide excellent control of powdery mildew, including Fontelis (penthiopyrad), Microthiol Disperss (wettable sulfur), Quintec (quinoxyfen), Procure (triflumizole), and Rally (myclobutanil).

Some new fungicides in development also provided outstanding control of powdery mildew which suggests that additional effective compounds may be available in the future.

Effectively managing powdery mildew with fungicides is best achieved by initial application before the first visible presence of the disease.

Good levels of disease control also can be obtained by starting applications after the first visible signs of powdery mildew. However, disease management success will decrease as the initial treatment is delayed and the disease becomes more established.

The risk of powdery mildew within a particular melon planting will be determined by the genetic susceptibility of the melon cultivar as well as environmental factors during the time of disease initiation and development.

Click this link to listen to Mike's Update [8]

Contact Matheron: (928) 726-6856 or [email protected] [9].

Lettuce injury symptoms can appear identical to those caused by other factors

By Barry Tickes, UA area agriculture agent

The three pre-emergence herbicides used in lettuce – Pronamide (Kerb), Benefin (Balan), and Bensulide (Prefar) - use the same mode of action to kill weeds. These are mitotic inhibitors and stop cell division and growth of the roots.

When lettuce is exposed to too much of these herbicides, root development is also inhibited. The symptoms of crop injury include stunting, marginal chlorosis, and death if the plant cannot recover. This is what you would expect from a plant that does not have roots to take up water and nutrients.

Anything that inhibits normal root development can produce the same symptoms. Some other conditions which can also cause poor root development, stunting, and chlorosis include excessive salts and fertilizer, soil compaction and crusting, and other conditions.

Salts inhibit the movement of water and nutrients into the roots. Sometimes water and nutrients are pulled out of the roots. Crop injury symptoms from salts resemble those caused by the herbicides, i.e. stunting, chlorosis and poor root development. Fertilizer contains salts and when in excess can cause similar problems.

Click this link to listen to Barry [10].

Contact Tickes: (928) 580-9902 or [email protected] [11].

Area-wide insect trapping network

By John Palumbo, UA research scientist and Extension specialist

Results of pheromone and sticky trap catches from Sep 7-29 can be viewed here [12].

Corn earworm: Flights have decreased across the region over the past two weeks. Numbers have been highest in Wellton and the south Gila Valley.

Tobacco budworm: Numbers have been light in all areas so far this fall with very low numbers caught in traps in Roll and Wellton.

Cabbage looper: Flight activity is on the increase and trap catches are definitely picking up in all traps. Activity last week was highest in Wellton and the south Gila Valley with activity increasing in the Yuma Valley.

Beet armyworm: Active since early September. Activity is especially heavy in the Gila Valley but declining in Wellton and Roll. Trap catches have been light in the Dome and Yuma Valleys thus far.

Whitefly: Sticky traps show that adult movement is decreasing in most areas, but increased considerably this past week in the south Yuma Valley.

Thrips numbers remain low in all trap locations.

 Listen to John's Update [13].

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