The weather remains warm and we're not out of danger from most fall insect pests. However, as temperatures begin to cool down in the next week or so, it is important that you not forget about Liriomyza leafminers, particularly as the first produce fields approach harvest. Leafminer numbers have been light-moderate thus far this season, but we have recently observed higher numbers (adults and larvae) showing up on the older leaves of lettuce here at the Yuma Ag Center. Much like last season, an increase in adult flies has been observed on yellow sticky traps used for monitoring whiteflies over the past week or so. In most cases, these traps have been located near or adjacent to fall melons, cotton or alfalfa. With temperatures forecasted to be in the 80 and 90s for the next week, leafminer adults should continue to be active, and larval activity could easily cause damage if left uncontrolled in lettuce or baby leaf fields where they are currently present. These larvae can cause significant damage to older, pre-harvest lettuce by feeding and damaging wrapper leaves of head lettuce and romaine. Pupae collecting within the leaf margins can also be considered contaminants. In addition, baby leaf lettuces, spring mixes and spinach are susceptible to larval feeding (mining) on the tender growing leaves. These populations can be effectively controlled with currently available products. Products that are presently being used to control armyworms, loopers and thrips such as, Radiant (5-7 oz/ac), Coragen (5-7 oz/ac) and Voliam Xpress (9 oz/ac), can effectively kill newly emerged larvae in the leaf mines before they cause significant damage. Similarly, Agri-Mek at 8-12 oz/ac can provide long residual control. Be sure to include a penetrating adjuvant with these products to enhance translaminar movement of the product and larval control. For more information on leafminer biology and management please go to "Leafminer Management".

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.

Based on last week’s weather, it’s officially summer in my book. Things seem to be slowing down, so I thought I’d change pace this week and take the opportunity to ask you, the readers of this newsletter, if there are any topics you are interested in hearing more about. I am happy to do some research and try to find some answers. Drop me a line at siemens@cals.arizona.edu or feel free to call me at 928.782.5869. I’d love to hear from you.

Yuma Weather

Clovers can be very difficult to control weeds here, but it is also a major crop and common ornamental. Clovers can survive under poor growing conditions and are not controlled with glyphosate and seem to get worse every year. There are more than 50 types and 300 species of clover and they can be easily misidentified. They are all in the legume (Fabracea) family and can use a bacterium (rhizobium) in the soil to convert nitrogen in the atmosphere to a form that they and other plants can use for fertilizer.    There are only 4 or 5 clover species that are agricultural pests here. The ones we get the most questions on are white and yellow sweet clover. These are in the Melilotus family. White sweet clover (Melilotus albus) is tall for a clover and can get 3 to 5 foot in height. The leaves are thinner than most clovers and this difficult to control weed lives at least 2 years and sometimes longer. Glyphosate and most of the contact herbicides do not control it. The plant growth regulator herbicides work best. Yellow sweet clover (Melilotus officinalis) is less common here. The flowers are yellow, and it is not as tall and vegetative as white sweet clover. Yellow is more common at higher elevations.   California burclover (Medicago polymorpha) and Black medic (Medicago lupina) are in the same genus as alfalfa and are more of a problem in landscapes, parks and golf courses than in agricultural fields here. They do not grow upright and spread below the crop or turf. The true clovers are in the Trifolium genus and include white and strawberry clover. These creep along the ground and root at the nodes of the stem. These are more of a urban landscape weed and not considered an agricultural problem. Creeping woodsorrel or Oxyalis looks like a clover but it is not related. It is a turf weed that spreads rapidly along the ground and can live for several years. Preemergent herbicides are effective against all these clovers before they become established. The postemergence herbicides that are most effective in controlling these clovers are the plant growth regulators. Contact herbicides and glyphosate are generally ineffective.

 Area wide Insect Trapping Network   VegIPM Update, Vol. 14, No. 1, Jan 11, 2023
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:             
CEW moth counts are down areawide average for this time of year. 
 
Beet armyworm:         
Trap counts increased in most ll locations; about average compared to previous years.
 
Cabbage looper:           
Cabbage looper counts increased in most traps and about  average for this time of season.
 
Diamondback moth:      
DBM moths continue to increase in all areas. About average for this time of the year.
 
Whitefly:                       
Adult movement light and is typical for this time of year. 
 
Thrips:                          
Thrips adult counts beginning to slowly increase in the past 2 weeks. Currently, below average compared with previous years.
 
Aphids:                        
Aphid movement increased significantly in North Yuma and Gila Valleys consistent with winds and storms. About average for early January.
 
Leafminers:                   
Adult activity up in many locations, and above average for January.