With the produce season essentially finished, it’s time to begin thinking about insect management in melons. Spring melon crops are rapidly growing, and so are insect pest populations. Cabbage loopers and leafminers are becoming evident in some areas, and PCAs should start ramping up their monitoring and sampling. More importantly, whitely populations are quietly becoming abundant on the spring melons of all sizes. Adults can easily be found on recently planted melons located at the Yuma Ag Center, and reports from local PCAs suggest that adult populations are beginning to show up on older plantings. As temperatures increase and crops/weeds mature, avoidance of excessive feeding from whitefly nymphs should be the primary concern on all melon types. Although CYSDV does occur in later spring melons, it is rarely yield limiting. But honeydew and sooty mold contamination on cantaloupes, mixed melons and watermelons can significantly reduce quality and marketability is whiteflies are not adequately controlled.  Our research has shown that to prevent fruit yield and quality losses on spring melons, a foliar insecticide treatment should be applied on threshold; that is, when average adult numbers exceed 2 per leaf when averaged across an entire melon field. At this level of adult abundance, immature populations are beginning to colonize. Timing sprays based on the adult threshold has been shown to significantly reduce the chance of yield / quality losses during spring harvests.  This threshold applies for the use of recommended IGRs (Courier, Knack, Cormoran, and Oberon), foliar applied neonicotinoids (Assail, Venom, Scorpion), neonicotinoid-like compounds (Sivanto prime and Transform), diamides, (Exirel and Minecto Pro) and the feeding disruptors (PQZ and Sefina).  For more information on whitefly management and available insecticides, go to these documents on Insect Management on Spring Melons: Whiteflies and Whitefly Control Chart-Spring Melons -2024. Also, be aware of honey bees and other pollinators in or around melon fields. If bees are present, be sure to carefully read labels and determine bee safety of a product before making an application in a melon field.  If applications are necessary during bloom, only apply a product that is considered bee safe (e.g., PQZ, Sefina, Sivanto, Assail). We also recommend that insecticides only be applied when honeybees are not actively working in the field (e.g. 10:00 pm – 3: 00 am).

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%). Lettuce was seeded, then sprinkler-irrigated to germinate seed on Nov 28, 2023 on double rows 12 in. apart on beds with 42 in. between bed centers.  All other water 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 Jan 17, 2024  at the 3-4 leaf stage to a 12-inch spacing. Treatment beds were separated by single nontreated beds. Treatments were applied with a tractor-mounted boom sprayer that delivered 50 gal/acre at 100 psi to flat-fan nozzles spaced 12 in apart.

Month	Max Temp (°F)	Min Temp (°F)	Average Temp (°F)	Rainfall
November	80	51	65	0.08 in
December	71	44	57	0.82 in
January	68	42	54	1.14 in
February	73	47	59	0.50 in

 
Powdery mildew (caused by Golovinomyces cichoracearum) efficacy trial treatments were made on February 15,2024, February 23, 2024, March 4, 2024, and March 12, 2024and .Disease was first seen on February  26,2024. Disease rating was done on March 15, 2024.   Disease severity was determined  by rating 10 plants within each of the four replicate plots per treatment using the following rating system: 0 = no powdery mildew present; 0.5 = one to a few very small powdery mildew colonies on bottom leaves; 1 = powdery mildew present on bottom leaves of plant; 2 = powdery mildew present on bottom leaves and lower wrapper leaves; 3 = powdery mildew present on bottom leaves and all wrapper leaves; 4 = powdery mildew present on bottom leaves, wrapper leaves, and cap leaf; 5 = powdery mildew present on entire plant. These ratings were transformed to percentage of leaves infected values before being statistically analyzed. Yield loss due to rejected lettuce heads would likely begin to occur on plants with a powdery mildew rating above 2.0 (percentage of leaves infected value of 40).         
The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. Most treatments significantly reduced the final severity of powdery mildew compared to nontreated plants. The most effective fungicides were Rhyme, Merivon, Quintec, Cevya, Luna Sensation, Luna Experience, and Elisys. 

Vegetation management with fire is a very old technique used in agriculture. It dates back to prehistoric times but is still used today. Fire is a part of nature and is necessary to maintain many grassland and forest ecosystems. It is used in this region primarily as a post harvest technique to remove dead or dormant plant material. It is most commonly used in the summer after grain is harvested to facilitate ground preparation for the next crop or in the spring prior to regrowth of bermudagrass to remove stubble and stimulate regrowth. One of the benefits of burning is that it can be effective in killing weed seeds. The effect of fire on weed seeds has been the subject of many studies and is dependent on many variables. These include the weed type and species, the depth of the seed in the soil, the heat of the fire and the duration of the fire.

The type and species of weeds that have been found to be most affected by burning are summer annuals. Weeds that produce seeds with hard seed coats are the least affected. These include sweet clovers, mallow, dodder, sesbania and others. Fire has little affect on creeping perennials, especially during the dormancy period. These include bermudagrass, field bindweed, perennial johnsongrass and nutsedge, all of which have below ground reproductive structures. In weeds that have become established, seedling grasses are more sensitive to fire than seedling broadleaves. This is primarily because the growing points of many grasses are below the soil while the growing points of broadleaves are above the soil and unprotected. Seeds that are burned before they become viable are also more sensitive to fire.

The depth of weed seed in the soil also will affect sensitivity to fire. In one study, 88% of the seed that was located in the top 1mm of soil was killed while only 18% of the seed buried 5 mm (0.19") into the soil was killed. Tillage following burning can also be expected to bring up viable seed.

The effect of temperature on seed viability has also been the subject of many studies. In most, the germination of summer annuals increased with rising temperature to about 140°F and dropped off rapidly as temperatures approached 212° F. Imbibed seeds were also more sensitive to fire than unimbibed seeds.

In addition to temperature, the duration of the fire has been found to affect seed mortality. Hot, slow fires kill many more weed seeds to greater depths than do light, flash fires that raise the temperature only in the top layer of soil. At one experimental site, wheat stubble with longer straw burned longer and hotter than stubble that was short.

 Area wide Insect Trapping Network   VegIPM Update, Vol. 14, No. 21, Oct 18, 2023           
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth increased in Tacna/Roll/Dome last week, and areawide about average for mid-October.
 
Beet armyworm:          
Trap counts highest in Tacna, Wellton and Dome, but below average for October.
 
Cabbage looper:         
Cabbage looper numbers increased in Tacna/Roll/Wellton but still below average.
 
Diamondback moth:    
DBM moths are beginning to appear in traps in Yuma Valley, trending below average for early October.
 
Whitefly:                      
Adult movement increased in the past 2 weeks and above average for mid-October.
 
Thrips:                         
Thrips adult activity down over the past week, and trending below average in October.
 
Aphids:                        
Winged adults continue to be captured for the season, consistent with heavy winds from W-NW. Can expect aphid flights to increase in the coming weeks.
 
Leafminers:                  
Adult activity increased significantly in Tacna associated with maturing melons. Trending above average for mid-October.