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).

Plant viruses cannot penetrate the intact plant cuticle and cellulose cell wall that acts as barrier to infection. The virus overcomes the problem by either avoiding the need to penetrate (example seed transmission) or by using the wound in plants as infection site, or transmission by insects, nematodes or fungi as a vector.  
 
Mechanical transmission involves the introduction of infective virus or viral RNA into the wounds of plants. Viruses such as Tobacco mosaic virus (TMV), Potato virus X are highly stable, and reach high concentration in plants.  As you all know TMV can readily contaminate hands, clothings, and implements and can be spread by worker. TMV can even spread mechanically by tobacco smokers as the virus is present in cured tobacco leaves. 
Mechanical transmission is of great importance.  In field and greenhouse, great amount of caution has to be implemented to not transmit the infection. Field sanitation, tool sanitation is very important to avoid the spread of virus. 
However, in experimental world mechanical transmission is a very useful tool to study viruses. Mechanical inoculation of virus to a heathy host plant is done for assays, to produce local lesions, in the propagation to of viruses for purification, in host range study, diagnosis, and to understand the interaction between virus and susceptible cells. 
 
 
Seed transmission:  About 1/7 th of the known plant viruses are transmitted through seeds. Different viruses have different host ranges (the plants that they can infect). Tobacco mosaic virus, Cucumber mosaic virus are some viruses with a very wide host range and they may not be seed transmissible in all plants they infect. Seed transmission plays a huge role in virus epidemiology. Not only they can be a primary source of infection, leading to an epidemic in the field upon conducible environment, seed transmission is an effective way for long distance travel of the virus, thus introducing the virus to new places. You have heard of USDA regulations/restrictions on different crops, from certain foreign countries to avoid introduction of infected seeds/plant materials. 
 
Seed transmission can occur simply by contamination of seeds, as in tomato seeds by Tobacco mosaic virus. This can be readily inactivated by seed treatments. 
The second type of seed transmission occurs when the virus is present in the embryo tissue that can happen prior to fertilization or takes place at pollination. Pea seed-borne mosaic virus is a well studied plant virus in this category. 
 
 
Pollen Transmisison:  Some viruses are transmitted from plant to plant via pollen. As in seed transmission, pollen transmission has two mechanisms, gametic infection of embryo and direct infection of mother plant. 
 
Vegetative propagation: An important horticultural practice, and unfortunately a very effective method for perpetuating and spreading viruses. In clonally propagated plants, an infected mother plant which could be asymptomatic could be used to make hundreds and thousands of daughter plants, which will all have the virus. Any vegetative parts  such as bulbs, corms, runners, and cutting will be infected. 
 
Grafting: Essentially a form of vegetative propagation, once the organic union has been established and plants (Scion and Stock) function as a single plant. In experimental front, grafting is used as a virus transmission methods, when all other methods fail.

Earlier this week, we initiated a trial examining the use of band steam for controlling Fusarium wilt of lettuce. The premise behind this research is to use steam heat to raise soil temperatures to levels sufficient to kill soilborne pathogens. For Fusarium oxysporum f. sp. lactucae, the pathogen which causes Fusarium wilt of lettuce, the required temperature for control is generally taken to be > 140°F for 20 minutes. Soil solarization, where clear plastic is placed over the crop bed during the summer, exploits this concept. The technique raises soil surface temperatures to 150-155˚F, effectively killing the pathogen and reducing disease incidence by 45-98% (Matheron and Porchas, 2010).

In our trials, we are using steam heat to raise soil temperatures. Steam is delivered by a 35 BHP steam generator mounted on a custom designed elongated bed shaper (Fig. 1). Preliminary results were encouraging. The device was able to increase the temperature of the top 3” of soil to over 180°F at a travel speed of 0.5 mph as shown in this video of the machine in action (shown below). These temperatures exceed that of those known to control pathogens responsible for causing Fusarium wilt of lettuce (> 140°F for 20 minutes).

Stay tuned for final trial results and reports on the efficacy of using steam heat to control Fusarium wilt of lettuce.

If you are interested in evaluating the technique on your farm, please contact me. We are seeking additional sites with a known history of Fusarium wilt of lettuce disease incidence to test the efficacy and performance of the device.

References
Matheron, M. E., & Porchas, M. 2010. Evaluation of soil solarization and flooding as management tools for Fusarium wilt of lettuce. Plant Dis. 94:1323-1328.

Acknowledgements
This project is sponsored by USDA-NIFA, the Arizona Specialty Crop Block Grant Program and the Arizona Iceberg Lettuce Research Council.  We greatly appreciate their support.

A special thank you is extended to Cory Mellon and Mellon Farms for allowing us to conduct this research on their farm.

Weeds are one of the most visible of all agricultural pests. They can’t move or hide and once established often stick up over the crop. Just one weed in a 10 acre field is annoying to look at. With insects and diseases, the damage is often more visible than the pest. That is not the case with weeds. A moderate weed infestation is approximately 10 weeds per square foot. If a herbicide produces 90% control, that leaves 1 weed per square foot or 43 weeds per acre. Without an untreated check, this can look like the herbicide failed!  It is easy to leave an untreated spot in a field and it is well worth doing. Many applicators do so unintentionally because of skips, powerlines and other causes. They help determine crop injury and weed control. Here are some examples of what various levels of control looked like from one of our cole crop trials:

Area wide Insect Trapping Network   VegIPM Update, Vol. 11, No. 21, October 14, 2020

Results of pheromone and sticky trap catches can be viewed here.

Corn earworm: Moth activity is above normal for early October ad has been steadily increasing since mid-September, particularly in Dome Valley and south Yuma Valley. 

Beet armyworm: Moths remain active throughout the desert, especially in Texas Hill and Dome Valley growing areas.

Cabbage looper: Cabbage looper activity remains unusually low for early October, likely a result of unusually hot weather. Larvae just starting to show up in some fields.   

Whitefly: Adult movement has been about average for this time of year. Activity highest in Wellton and Roll near fall melons.

Thrips: To date, thrips activity has been seasonably low at all trap locations; most activity found in Bard.  Numbers beginning to slowly trend upward

Aphids: Aphids have been caught in only one trap thus far (Bard). Normal for this time of year.  Still early, anticipate they will begin to show up in heavier numbers in mid-late October.

Leafminers: Adult activity below normal for September, but moderate numbers caught in Wellton and south Gila Valley in areas where cotton was recently harvested and disked under.