Seems like each year about this time we begin to think how unusual this produce season is compared to previous years. Of course, every season is different. That’s the complicated nature of farming and pest management; so many factors (some explained and many unexplained) influence plant growth and insect pest activity and abundance. I thought I’d share some of my recent observations of “unusual” insect activity from research plots at the Yuma Ag Center (YAC), local commercial fields and conversations with PCAs. Whitefly populations were the lightest we’ve seen in years, but have been heavy in a few small areas. Many, like myself, believe this is due to the lower cotton acreage this summer, but there could be other factors as well. Beet armyworm pressure remains steady, but seems much lower than what I usually see this time of the year. Cabbage looper numbers have been considerably lower from what we typically see in lettuce and cole crops in October. There numbers seem to be increasing now. Corn earworm larvae populations appear to be about normal relative to the past 3 or 4 years. So far, I have not had any complaints in regards to controlling these worm pests, and all the standard Lep materials are performing up to par in my efficacy trials. In contrast, diamondback moth larvae are very abundant in my broccoli trials. They showed up earlier and in higher numbers than I typically see this time of the year. Not sure why? Good news is, they remain easy to kill with standard materials. Another interesting pest showing up is the Hawaiian beet webworm. They were very abundant last year and PCAs have been sending me images from this season (see image below). The larvae prefer spinach and beets and can cause damage if left untreated. Again, easy to control. Western flower thrips are on the increase, consistent with the warm weather. Adult and immatures are increasing on my lettuce plots, and several PCAs have mentioned that they are quite abundant. Have also had some reports of cowpea aphids showing up in lettuce. Experience has shown us that cowpea aphid will begin to colonize lettuce about this time of the year, but never seems to amount to much and colonies disappear when it gets colder. If the weather breaks in the next week or so as anticipated, worm and thrips pressure should slow down considerably. However, given our current and predicted El Nino weather pattern, all bets are off. So, have your weather reports handy, and keep your eyes open for the unexpected. Remember: When in Doubt-Scout. 

This study was conducted at the JV farms at Gila Valley. Lettuce variety ‘Guapo’ was seeded, then sprinkler-irrigated to germinate seed on September 19, 2023, on double rows 12 in. apart on beds with 42 in. between bed centers.  Rest of the irrigation was supplied by furrow irrigation or rainfall. Treatments were replicated five times in a randomized complete block design. Each replicate plot consisted of 25 ft of bed, which contained two 25 ft rows of lettuce. Plants were thinned on October 9, 2023 at the 3-4 leaf stage to a 12-inch spacing. Treatment beds were separated by single nontreated beds. Treatments were applied by incorporating in soil before seeding or with a tractor-mounted boom sprayer that delivered 50 gal/acre at 100 psi to flat-fan nozzles spaced 12 in apart.

Month	Max	Min	Avg	Rain
September	100	71	86	0.71 in
October	93	61	77	0.00 in
November	80	51	65	0.08 in
December	71	44	57	0.82 in

 
Fusarium wilt (caused by Fusarium oxysporum f. sp. lactucae ) rating was done in the field by observing the typical symptom of lettuce wilt. Confirmation was done by cutting the cross section of roots. Disease scoring/rating was done on December 6, 2023. 
 
The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. The disease pressure was extremely high in 2023, and most treatments showed little or no control against the disease. The treatments that showed some activity were Bexfond, Cevya, Rhyme, and Serifel. Plant vigor was normal and phytotoxicity symptoms were not observed in any treatments in this trial.

Last winter, we initiated two trials investigating the use of band-steam for controlling Sclerotinia lettuce drop and weeds in lettuce. Band-steam is where steam is used to heat narrow strips of soil to levels sufficient to kill soilborne pathogens and weeds (>140 °F for > 20 minutes). Trial results were promising and summarized in a pre-recorded presentation prepared for the 2021 ASABE Annual International Meeting. Highlights included finding that treatment with steam provided better than 85% weed control, and the unexpected result that crop yields were improved by more than 24% (Table 1). Energy requirements were high and treatment costs were more than $650/acre. We concluded that band-steam may be a viable technique for controlling soilborne pests in high value vegetable crops if the significant yield increases found in the study can be realized. For all the nitty gritty details and to see the presentation, click here or on the links below.
 

	Weed Density	Weed Control	Hand Weeding Time	Head Weight	Marketable Heads	Marketable Yield
Treatment	(no. ac-1)	(%)	(hr ac-1)	(lb head-1)	(%)	(lb ac-1)
Band Steam	9,148 b1	86	7.7 b	1.60 a	80 a	32,909 a
Non-treated	65,713 a	0	10.4 a	1.46 b	69 b	26,521 b
*Means within columns followed by the same letter are not significantly different according to Duncan’s New Multiple Range Test (P=0.10)

Fig. 1. Click on the image to see a presentation on the development and
evaluation of a novel band-steam applicator for controlling soilborne pathogens
and weeds in lettuce.

Dodder has been a difficult to control weed in this area for a long time, but it seems to be getting worse in recent years. It is listed as one of the 10 most problematic weeds in the U.S. by the Department of Agriculture. There are more than 150 species of dodder. Fifteen of these can be found in Arizona, 3 are common and one, field dodder (Cuscuta campestris), is a problem in the lower Colorado River region. It can be a problem on many crops grown during the summer months including melons, safflower, asparagus, sugar beets, beans, alfalfa and others. Dodder is one of the most unusual weeds we have to deal with. It is a parasitic annual that has no leaves or roots after it is attached to a host. It obtains all of its energy from the plants it attaches to. Dodder germinates near the soil surface and lives off of food reserves in the seed. It must attach to a host within 5 to 10 days or it will die. After it has found a suitable host, it produces adventitious roots called haustoria that grow into the vascular system of the host plant. After it is attached, the lower portion of the dodder seedling dies and all contact with the soil ends. Dodder seed is small, about 1/16 inch in diameter, and germinates in the spring or summer once the soil temperature reaches about 60 degrees. Each plant can produce several thousand seeds. The seed is hard and less than a third can germinate the following season. The remainder can remain dormant but viable for 20 years or more. The seed is small and light enough to float in water and blow in the wind. Most of the movement is probably from contaminated crops, seed and equipment. Controlling this weed starts by reducing seed movement into an area. Most states and countries have laws that prohibit the import of dodder seed. Only certified seed should be planted. A major cause for the spread of dodder in Arizona has been in non- certified alfalfa seed. Once it is present in a field, annual crops that are poor hosts can reduce the spread of this weed. Poor host crops include grasses, grains, and other monocots. Other weeds can serve as hosts and should be eliminated. Preemergent herbicides can be effective in keeping this weed from becoming established. Postemergence herbicides need to at least temporarily destroy the host. Perennial crops, like alfalfa, can be temporarily burned to the ground with contact herbicides like Gramoxone, Chateau or Scythe plus an adjuvant. Dodder can be selectively killed with glyphosate in Roundup Ready Alfalfa. The most effective control is with preemergent herbicides. These include trifluralin, pendimethalin, benefin, acthal and others. When the level of these herbicides has dropped to sub-lethal amounts, dodder seed will germinate and survive. Repeated applications are normally required.

 Areawide Insect Trapping Network   VegIPM Update, Vol. 15, No. 16, Aug 7, 2024
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth counts decreased areawide; about average to previous years.
 
Beet armyworm:        
BAW moth counts decreased; comparable to previous summers.
 
Cabbage looper:         
Cabbage looper numbers are low consistent with previous years and higher temperatures.
 
Diamondback moth:     
DBM moths were not caught in any trap; average for this time of the year.
 
Whitefly:                     
Adult movement continues to decrease, average for this time of the year.
 
Thrips:                          
Thrips adult activity continues to decline, average for early August.
 
Aphids:                       
Aphid movement is absent and consistent with what we typically see during the summer.
 
Leafminers:                   
Adult activity declining and below average for early August.