You may have noticed in the past week or so the increase in insect activity on local crops. In general, insect activity has been relatively light to moderate this spring largely due to the cool weather we experienced in March and April. The exception has been the widespread incidence of seedcorn maggots affecting melon and cotton stands over the past month. The occurrence of the maggots was consistent with the cool and wet conditions we experienced this spring, and the addition of extra organic matter (i.e., manure, heavy produce residue) in fields did not help matters. Within the past week, numbers of whitefly adults and cabbage looper larvae have increased on our melon crops at the Yuma Ag Center. As we start to experience the hot and dry weather typical in May and June one can expect insect activity to increase. That is because local weather patterns have a significant impact on the abundance of insect pests in our crops. Components of weather, mainly temperature and moisture, can either promote insect population growth or cause populations to decline. For a more detailed explanation on the impact of weather on insects 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.

Dacthal was first registered in 1959 but like most older products that are still used, we are constantly adapting it to our changing cultural practices. Dacthal is a mitotic inhibitor and kills germinating weeds by stopping cell division. This is the same mode of action as many other preemergence herbicides such as Trifluralin, Prowl, Balan, Kerb and others but its chemistry and how it moves in the soil and plant are different. Dacthal is absorbed by both shoots and roots of germinating seedlings although most of the activity is from shoot absorption. When absorbed by the shoots, it will move upward into the plant. It is not absorbed by foliage and can be safely applied over the crop. Dacthal has a strong affinity for soil and adsorbs strongly to soil particles. If Dacthal is applied to dry soil, it sometimes will not work because the herbicide it stuck on the soil and not available to kill weeds. Conversely, if the soil is saturated, it may not be adequately incorporated. The best time to apply Dacthal is when the soil is moist but not saturated.

When Dacthal was first being developed it was tested for use on lettuce. If it is sprayed on or chemigated it will cause severe injury to lettuce. If it is mechanically incorporated it is surprisingly safe to lettuce. It is fairly broad-spectrum bur weak on mustards.

Area wide Insect Trapping Network   VegIPM Update, Vol. 12, No. 15, Jul 28,  2021
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth counts decreased significantly since mid-June comparable to what we observed last summer.
 
Beet armyworm:         
Trap counts remain low in most locations  and are trending similar to last summer.
 
Cabbage looper:         
Cabbage looper numbers remain low consistent with the lack of activity this fall and summer compared to last season.
 
Whitefly:                     
Adult movement continuing to increase rapidly, particularly in Wellton and Dome Valley consistent with the termination of spring melons.
 
Thrips:                          
Thrips adult movement continuing to decline to numbers comparable to this time last year.
 
Aphids:                        
Aphid movement has been absent for the past 2 months typical with high summer temperatures.  
 
Leafminers:                 
Adult activity slightly above for mid-summer.
 
Diamondback moth:    
DBM trap counts have been zeroed out in all trap locations for all of July consistent with trends observed over the past 5 years.