As growers have begun planting fall melon crops and with produce planting a few weeks away, PCAs are likely to encounter a number of insects that have the potential to cause serious economic losses to seedling crops during stand establishment. These include flea beetles, crickets (sometimes grasshoppers), darkling and rove beetles, and saltmarsh caterpillars. These insects all have chewing mouthparts and most are capable of consuming large amounts of leaf tissue in a short time. Seedling crops at the cotyledon stage are most susceptible to these pests, where feeding by large numbers can devour much of the cotyledons or outright kill the small plants. If left uncontrolled, larger seedling plants (2-4 leaf stage) can sustain significant feeding damage on the terminal growing points or newly emerged leaves. Not only can this feeding stunt plant growth, but can result in lack of uniformity and maturity at harvest. Host sources of flea beetle, cricket and "wooly worm" infestations include numerous summer crops (e.g., sudan grass, cotton and alfalfa) and a large host of weeds (e.g., purslane). Experience suggests that melon fields planted adjacent to these crops/weedy areas are at a high risk from these seedling pest, and particularly flea beetles. As these summer host plants are harvested or terminated during the next several weeks, these seedling pests typically move to the next available host crop - lettuce, cole crops and melons. Fortunately, there are many registered insecticide alternatives available that can be applied via sprinkler chemigation (i.e., pyrethroids) or foliar sprays (i.e., Lannate, neonicotinoids) that can cost-effectively minimize their abundance and damage to emerging crops. For more information on insect pests of leafy vegetables and melons at stand establishment go to this link.

This study was conducted at the Yuma Valley Agricultural Center. The soil was a silty clay loam (7-56-37 sand-silt-clay, pH 7.2, O.M. 0.7%). Spinach ‘Revere’ was seeded, then sprinkler-irrigated to germinate seed Jan 18, 2024 on beds with 84 in. between bed centers and containing 30 lines of seed per bed.  All irrigation water was supplied by sprinkler irrigation.  Treatments were replicated four times in a randomized complete block design.  Replicate plots consisted of 15 ft lengths of bed separated by 3 ft lengths of nontreated bed.  Treatments were applied with a CO₂backpack sprayer that delivered 50 gal/acre at 40 psi to flat-fan nozzles. 
 

Month	Max	Min	Average	Rainfall
January	68	42	54	1.14 in
February	73	47	59	0.50 in
March	77	50	63	0.31 in

 
Downy mildew (caused by Peronospora farinosa f. sp. spinaciae) was first observed in plots on Feb 19  and final reading was taken on February 26, 2024. Spray date for each treatments are listed in excel file with the results.   Disease severity was recorded by determining the percentage of infected leaves present within three 1-ft² areas within each of the four replicate plots per treatment.  The number of spinach leaves in a 1-ft² area of bed was approximately 144. 

The data (found in the accompanying Excel file) illustrate the degree of disease reduction obtained by applications of the various tested fungicides. Products that  provided effective control against the disease include Orondis ultra, Thrive 4 M, Fungout, Cevya, Eject and Zampro. No phytotoxicity was observed in any of the 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. 13, No. 17, Aug 24, 2022
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:           
CEW moth counts increased slightly in the past 2 weeks, about average for late summer
 
Beet armyworm:         
Trap counts stay active in some locations (Yuma Dome Valley and Wellton) particularly near alfalfa.
 
Cabbage looper:          
Cabbage looper numbers remained low consistent previous years.
 
Diamondback moth:     
DBM moths not active in any trap since June; average for this time of the year.
 
Whitefly:                       
Adult movement decreased in past 2 weeks consistent with previous years
 
Thrips:                          
Thrips adults decreasing in most locations, and trending comparable to previous years.
 
Aphids:                        
Aphid movement is absent and consistent with what we typically see during the summer.
 
Leafminers:                   
Adult activity tending downward, average for early late August