The latest Arizona Vegetable Integrated Pest Management Update from the University of Arizona (UA) Cooperative Extension in Yuma, Ariz., released June 13, 2012.

Plan now for whitefly management on fall produce, melons

By John Palumbo, UA Research Scientist and Extension Specialist

The spring melon harvest is well under way. It is important to think about whitefly management in fall produce and melons crops.

The first line of defense to avoid whitefly issues in fall produce and melon plantings is for pest control advisers and growers to be vigilant in their whitefly management program on cotton this summer. This is particularly important since there appears to be a large acreage of Arizona cotton grown this year.

Before whitefly management begins in cotton, it is important to prevent whitefly populations from building up to large numbers in spring melons during harvest or recently completed.

In surveying melon crops for Cucurbit Yellow Stunting Disorder Virus (CYSDV) this spring, it was apparent that, similar to last year, a large proportion of the spring melon acreage throughout the area was grown near cotton.

UA surveys show on an area-wide basis that more than 70 percent of the melon acreage this spring was planted adjacent to or within one-quarter mile of cotton (see 2011-2012 Melon CYSDV Survey).

In the Gila Valley, about 84 percent of the melon acreage was grown adjacent to cotton. In the Yuma Valley 60-percent plus of the melon acreage is near cotton.

Although whitefly numbers were relatively light this spring, increased whitefly numbers have been observed over the past week in melons, coinciding with higher temperatures and area-wide melon harvests.

Proper sanitation in spring melons is essential to avoid unnecessary whitefly problems in cotton. Melon growers should quickly destroy plant residue as soon as possible following harvest.

A delay in disking under melon fields after harvest can provide a large source of adult whiteflies that will readily disperse into cotton especially since they do not need to fly very far. Whiteflies may also move into nearby weeds; many of which are hosts for the CYSDV.

These plants also potentially extend the host-acquisition period for CYSDV. This may be important since the CYSDV in spring melons incidence (albeit at non-economic levels) has been relatively high this year, particularly in the Dome Valley-Wellton area (see attachment).

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Remember when in doubt – scout.

Contact Palumbo: (928) 782-3836 or jpalumbo@ag.arizona.edu.

Sudden wilt and death of melon plants

By Mike Matheron, UA Extension Plant Pathologist

Temperatures are increasing, melon plantings are maturing, and sometimes sudden wilt and the death of plants occurs.

What is causing this condition?

In the desert production areas of Arizona and California, the symptoms of melon plant wilting and collapse usually are attributed to one of four diseases - Charcoal rot, Fusarium wilt, Monosporascus root rot and vine decline, or Pythium sudden wilt.

Each disease is caused by a different soil-borne plant pathogen so knowing the management options available first requires an accurate identification of the responsible pathogen.

Charcoal rot, Fusarium wilt, and Monosporascus rot and vine decline, caused by Macrophomina phaseolina, Fusarium oxysporum, and Monosporascus cannonballus, respectively, are not effectively controlled by fungicides at this time.

Preventative actions which may lessen the severity of these diseases include planting resistant melon varieties when available (for Fusarium wilt) and minimizing plant stress. Plant stress due to over- or under-irrigation can be managed. Other crop stresses due to fruit load and hot temperatures are obviously beyond your control.

The other disease mentioned, Pythium sudden wilt, was associated with significant losses of plants last season in several watermelon plantings. Pythium is a fungus-like pathogen that can be managed by fungicides including mefenoxam.

The difficulty in preventing extensive Pythium sudden wilt is that once the disease is initially detected in a field, the rapid deployment of an effective fungicide treatment will protect non-infected plants but may not save plants already infected but not yet displaying sudden wilt symptoms.

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Contact Matheron: (928) 726-6856 or matheron@ag.arizona.edu.

Nutsedge control with Eptam and summer fallow

By Barry Tickes, UA Area Agriculture Agent

Nutsedge is one of the most difficult to control weeds in Arizona and worldwide. It is a perennial that spreads vegetatively with below ground tubers which can remain viable for many years.

Yellow and purple nutsedge are common throughout Arizona. Most of it is purple which is the more difficult to control of the two.

There are few herbicides which will completely control nutsedge. It is so prolific that even fairly high levels of control last only one season. Most herbicides should be used for several consecutive years to keep this weed in check.

When nutsedge infestations get worse every year, it can help to combine summer fallow with chemical treatment to break the cycle and get the problem under control.

One of the most effective and economical treatments for nutsedge control is Eptam (EPTC) combined with summer fallow. This technique can be highly effective but can also completely fail if proper application and cultural practices are not followed. The product was developed 25 years ago but is still often misunderstood.

The following six principals are important for this technique to be effective.

1 - Above ground shoots and below ground tubers must be destroyed. Emerged shoots will provide nutrients for the production of new, below-ground tubers. Viable below-ground tubers will produce new rhizomes, basal bulbs, and above ground shoots.

Tillage and some herbicides including glyphosate can destroy above ground shoots. The Eptam fallow treatment will destroy rhizomes attempting to reach the surface.

2 - Eptam is one of the most volatile herbicides available. It is lost in several ways including microbiological and photochemical decomposition but the most common means of losing EPTC in the irrigated Southwest is by contact with water. It volatizes from irrigation water, off of wet soil, and is leached deep into the soil.

EPTC should be incorporated into dry soil to remain active for a much longer period of time. It should not be irrigated after application unless the objective is to move it down to contact deep tubers or to remove it in preparation for the planting of a susceptible crop.

3 - Eptam works on the nutsedge plant parts trying to grow (rhizomes and shoots). It works best on stressed plants but will have no effect on nutlets that are dormant.

Enough moisture should be made available to stimulate nutsedge growth but under stressed conditions. An irrigation cycle may be necessary. Once the top six inches is dry, Eptam should be applied and incorporated.

4 - A chemical tarp is created with the surface application of Eptam that prevents shoots and rhizomes from reaching the surface. The surface should be left as smooth as possible. Any untreated areas or breaks in the surface from implements, wheels, or even footprints will allow shoots to emerge.

5 - Eptam should not be applied too early (April or May) because of possible degradation prior to the period of rapid nutsedge growth or too late (August or September) because of decreasing growth and potential injury to fall planted crops.

6 - To avoid injury to following crops, irrigate at least 30 days prior to planting. The Eptam label specifies “Do not plant cotton or crops not listed on the Eptam label for 90 days after application.”

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Contact Tickes: (928) 580-9902 or btickes@ag.arizona.edu