Arizona Veg IPM Update: Insect activity, fusarium wilt, weed control

Arizona Veg IPM Update: Insect activity, fusarium wilt, weed control

The bagrada bug population has been heavy this year in low-desert-grown cole crops in southwestern Arizona and California's Imperial Valley.  Pest control advisers are still actively battling the bagrada bug, especially in Bard (Calif.), and Arizona's Gila and Yuma valleys.  

The Arizona Vegetable Integrated Pest Management Update from the University of Arizona (UA) Cooperative Extension in Yuma, Ariz. released Oct. 16, 2013.

Insect activity remains steady

By John Palumbo, UA research scientist and Extension specialist

The recent break in the weather suggests that insect activity in general should begin to significantly decline throughout the region. In the Yuma Valley during the last 10 days, temperatures have been on average about 7 degrees cooler than normal. Nighttime temperatures have been up to 12 degrees cooler.

However based on insect activity observed in experimental plots at the Yuma Agricultural Center (YAC), plus reports from pest control advisers, this is not the case. In September, whitefly, beet armyworm and bagrada bug activity were heavy in most areas.

We saw a small decline in whitefly activity following the rains one month ago, but adults are still actively moving in some areas.

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At the YAC, whiteflies on untreated melons were causing significant plant mortality from heavy immature colonies and cucurbit yellow stunting disorder virus. Beet armyworm pressure started heavy in September and remains heavy in our untreated blocks. We are still observing overlapping egg laying of egg masses and cabbage looper eggs.

As is typical, cabbage loopers are very active now as witnessed by large larval populations in YAC plots and an area-wide increase in trap captures of moths. We are also picking up a significant increase in leafminer activity on untreated lettuce plots which is consistent with this time of the year.

The bagrada bug population has been heavy this year and pressure remains high in the YAC experimental plots. The bug movement has not yet subsided. Reports coming in from PCAs suggest they are still actively battling the bagrada bug in cole crops, especially in Bard, and the Gila and Yuma Valleys.

A new planting of broccoli on Oct. 10 at the YAC was heavily infested with adults upon plant emergence. On older plantings, nymph and adult populations were widespread.

Based on past experiences, we do not expect a significant decline in bagrada activity until average temperatures drop below 70 degrees.

Finally, consistent with the heavy north-northwest winds experienced last week, we are picking up winged aphids in sticky traps - albeit in low numbers - in the Gila and Yuma Valleys.

We have not detected winged aphids or colonies on winter vegetable plants yet. Temperatures in mid-October were average for this time of the year, and are expected to be slightly higher than normal for the next seven-plus days.

Do not be surprised if insect activity continues at the same pace until the next break in the weather which is historically around the opening of deer season, Nov 1. Life is good!

Listen to John [5].

“Remember, when in doubt - scout.”

Contact Palumbo: (928) 782-3836 or [email protected] [6].

Fusarium wilt on lettuce

By Mike Matheron, UA Extension Plant Pathologist

Fusarium wilt has been found annually in lettuce fields from mid-October through early January since the first discovery of the disease in Arizona during the 2001-02 growing season.

The initial visual indication of the disease is the yellowing of one or more older leaves, followed by leaf wilting and death.

The external root surface is unaffected. However, a brown-to-black necrosis of the internal taproot and crown tissue will be apparent. Disease incidence can range from a few plants up to large areas or zones of infected plants within a field.

Plants can become infected and display symptoms at any age, ranging from very young plants just after thinning to those ready for harvest.

Symptoms of Fusarium wilt resemble two other lettuce disorders: ammonia toxicity and the early stages of lettuce drop. To confirm disease identity, it is necessary to bring plant samples to me at the YAC for analysis.

Confirmation of disease identity is achieved by isolation and identification of the causal fungus of Fusarium wilt of lettuce, Fusarium oxysporum, f. sp. lactucae, from symptomatic root tissue.

Disease development is largely affected by planting date and the type of lettuce grown. The main determinant of disease severity with respect to planting date is the soil temperature.

Research data demonstrate that lettuce planted in early September can result in high levels of Fusarium wilt. Plantings in the same naturally-infested field started in mid-October or early December sustain moderately low and trace levels of disease, respectively.

Of many crisphead and romaine cultivars tested, crisphead cultivars generally are significantly more susceptible to Fusarium wilt than romaine lettuce. The lettuce Fusarium wilt pathogen can survive in soil for many years. Minimizing the spread of infested soil within and especially between fields is of paramount importance.

Two comprehensive research reports concerning disease development and management of Fusarium wilt of lettuce are available. Please contact me and I will e-mail the reports to you.

Click link to Mike's Update [7].

Contact Matheron: (928) 726-6856 or [email protected] [8].

Cole crop weed control

By Barry Tickes, UA area agriculture agent

Dacthal, Prefar, and GoalTender are the primary herbicides used in the low deserts on broccoli and cauliflower.

Other options include Trifluralin (Treflan), Devrinol, Stinger, Poast, and Select. All of these herbicides have different characteristics and should be used differently for maximum weed control and crop safety.

Dacthal (DCPA) is effective only when applied prior to weed emergence but does not prevent weed seed germination. It is absorbed at the growing points between the radicle and cotyledon leaves. This is called the coleoptile on grasses and the hypocotyl on broadleaf weeds. Weeds sometimes emerge but stop growing.

To be effective, this herbicide should be concentrated near these growing points. It sticks well to the soil and needs a fair amount of water to incorporate it when using sprinklers. Furrow irrigation works as well if the bed tops are thoroughly moistened.

Applying Dacthal to dry soil and incorporating it with light amounts of sprinkler or furrow water does not work. It works best when the soil is moist at application. Dacthal is fairly broad spectrum but is weak on mustards, sunflower, and the thistle family.

Prefar (Bensulide) also adheres well to the soil but works at the root tips. Dacthal and Prefar are not systemic and move very little in plants. These products only work where the roots and shoots contact them.

Prefar must be incorporated with large amounts of sprinkler water or chemigated. Furrow irrigation, even when it thoroughly moistens the bed, will not incorporate this herbicide on most soils.

Prefar is best on grasses, purslane, and pigweed, and will control lambsquarters and goosefoot in some situations.

GoalTender (Oxyfluorfen) differs greatly from Dacthal and Prefar. It works primarily on the foliage, even when used as a pre-emergence herbicide. It is used pre-emergence and postemergence and has no activity on roots or shoots.

GoalTender inhibits the production of an enzyme in the plant which leads to the destruction of cell membranes. It is fast acting, dependent on sunlight, and acts like a contact herbicide.

Even when used pre-emergence to the weeds, it is dependent on sunlight and the weeds must emerge from the ground. The weeds absorb the herbicide at emergence and twice the postemergence rate is normally required.

Since a barrier is created on the surface, any disturbance of the soil after application can reduce control.

Click link to listen to Barry [9]

Contact Tickes: (928) 580-9902 or[email protected] [10].

Insect activity - the latest findings

By John Palumbo, UA research scientist and Extension specialist

Results of pheromone and sticky trap catches from Sep 29-Oct 12 can be viewed here [11].

Corn earworm: Flight activity continues to decline and has decreased across the region over the last two weeks. Numbers remain highest in Wellton.

Tobacco budworm: Numbers continue to be light in all areas thus far this fall with very low numbers caught in traps in Wellton.

Cabbage looper: Flight activity increased in all areas. Activity last week was highest in the north Gila Valley, Wellton, and the south Yuma Valley.

Beet armyworm: Has been active since early September. Activity is especially high in Wellton, the Gila Valley, and the south Yuma Valley.

Whitefly overall - Sticky traps indicate that adult movement is decreasing in most areas, but increased considerably in early October in the north Gila Valley and the mid-Yuma Valley.

Thrips numbers remain low in most trap locations but increased significantly in Roll over the last two weeks.

Aphids: Winged aphids were picked up in low numbers in sticky traps in the north Gila and south Yuma Valleys. The species were unknown, but were not aphids known to colonize winter vegetables (e.g., green peach aphid).

Listen to John [12].

Contact Palumbo: (928) 782-3836 or [email protected] [6].

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