We have historically ended our Areawide Pheromone and Sticky Trap monitoring for insects around the first of April as the produce season ends. Beginning last year however, we continued our Areawide Trapping Network throughout the summer and are doing so now to continue to collect trapping data from all 16 areawide trap locations year-round.  So why is this additional trapping data useful? For several reasons. First, understanding the activity of some of our key pests when produce is not available (during the summer) may give us an indication of what to expect as the fall produce season begins. This may be particularly helpful for predicting moth flights and whitefly flights in August-September coinciding with early transplanting and direct seeded crops.  Another example is keeping track of corn earworm which can unexpectedly show up near the beginning of fall harvests. Secondly, trapping for pests during the summer has shown us that 2 of our more important produce pests are not caught in traps during the summer. We presume this is due to the absence of brassica crops and weeds for diamondback moth, and high daytime temperatures lethal to aphids. The fact that trap catches resume in the fall supports our conclusion that these pests are absent in the summer, only to reenter the desert via winds and/or transplants in the fall. And finally, it gives me something to do in the summer.  So, visit the Areawide Summer Trap Network if you’re curious what our key pests are up to. We also taken on another interesting project to monitor thrips activity during the summer. This involves plant sampling using a dislodgement sampling method (beat pan) to determine the relative abundance of thrips adults and larvae on alfalfa, cotton, melons, wheat, Sudan grass, and weeds.  This is being conducted to supplement our yellow sticky trap data that only indicates thrips adult flight movement an area. With this plant sampling we should be able to determine the primary host plants thrips are colonizing in the cropping season during the long hot summer. We are also trying to determine whether these crops allow for the reproduction of thrips. So far, all the crops and weeds we have sampled have shown that thrips will reproduce and complete their life cycle on them. This is important, particularly for weeds, as we are trying to determine whether INSV can be survive the summer in the absence of lettuce. It is also important because it allows us to determine potential exposure of thrips to key insecticides like Radiant and Lannate for resistance management purposes. These crops essentially serve as untreated refugia that likely sustains insecticide susceptibility and is the reason these products are still effective against thrips.  We will be conducting this work throughout the summer, as well as through next produce season. We will be providing data in each Veg IPM update. For the most recent sampling data see our Areawide Thrips Monitoring.  As always, if you have any ideas on thrips monitoring or insect trapping, we’d be glad to listen and discuss. As my dad used to say, “to solve the problem, you must first understand the problem”. 

Fusarium wilt of watermelon, caused by Fusarium oxysporum f. sp. niveum,  is one of the oldest described Fusarium wilt diseases and the most economically important disease of watermelon worldwide. It occurs on every continent except Antarctica and new races of the pathogen continue to impact production in many areas around the world. Long-term survival of the pathogen in the soil and the evolution of new races make management of Fusarium wilt difficult. 
In 2022, we had  a lot of watermelon fields infected with Fusarium from Winterhaven to Yuma, Wellton, and Mohawk Valley. Rain, and overwatering of fields when plants set fruits might have contributed to the disease development. It is always a good idea to look out for any potential diseases that might occur this year! 
 
Symptoms of Fusarium can sometimes be confused with water deficiency, even though there is plenty of water in the field. In Yuma valley we have seen fusarium problem in some overwatered fields. 
Initial symptoms often include a dull, gray green appearance of leaves that precedes a loss of turgor pressure and wilting.  Wilting is followed by a yellowing of the leaves and finally necrosis.  The wilting generally starts with the older leaves and progresses to the younger foliage. Under conditions of high inoculum density or a very susceptible host, the entire plant may wilt and die within a short time.  Affected plants that do not die are often stunted and have considerably reduced yields.  Under high inoculum pressure, seedlings may damp off as they emerge from the soil. 
 
 Initial infection of seedlings usually occurs from chlamydospores (resting structure)  that have overwintered in the soil.  Chlamydospores germinate and produce infection hyphae that penetrate the root cortex, often where the lateral roots emerge.  Infection may be enhanced by wounds or damage to the roots.  The fungus colonizes the root cortex and soon invades the xylem tissue, where it produces more mycelia and microconidia.  Consequently, the fungus becomes systemic and often can be isolated from tissue well away from the roots. The vascular damage we see in the roots is the defense mechanism of the plant to impede the movement of pathogen. 
 
Disease management include planting clean seeds/transplants, use of resistant cultivars, crop rotation, soil fumigation, soil solarization, grafting, biological control. An integrated approach utilizing two or more methods is required for successful disease management.

Glyphosate has long been a popular product for non-selective weed control around fields. It is an effective treatment and the regulations for this use are reasonable. There has been much public concern in recent years, however, about the safety of this herbicide to human health. Some countries and U.S. municipalities now have strict regulations for Glyphosate use. Whether they are warrened or not, these concerns have caused growers to look for alternatives.

Glyphosate is popular for use around fields because it is 1) broad spectrum and will kill both grasses and broadleaf weeds, 2) is not active in the soil and will not wash into fields, 3) is not volatile and with not lift off and move into fields and 4) is affordable even in low value crops.

We evaluated 15 herbicides this season to determine how well they would fit these criteria. These included herbicides that used 5 different modes of action to kill weeds. The trials were conducted between October and December this year at the Yuma Agriculture Center. The herbicides that were tested and their mode of action are listed in the table below.

Weed Control
The weeds that were present in these trials were nettleleaf goosefoot, lambsquarters, common purslane, summer annual grasses and winter annual grasses. The following graph illustrates the levels of control we achieved with these weeds compared to Glyphosate. 

There were only 3 of the tested products that controlled all of these weeds as well as Glyphosate (arrows). These were Paraquat (Gramoxone), Salflufenacil (Sharpen) and Glufosinate (Liberty,Rely). Several of the others were good on broadleaves but weak on grasses. This could be overcome by combining them with a grass herbicide.

Soil Residual
One of the characteristics of Glyphosate that make it so popular is that it does not stay around in the soil except in very rare situations. Soil gets moved around with equipment,wind and water and soil activity can be a negative even on field edges. Soil residual herbicides are commonly used here but most have fairly short activity. We planted wheat, lettuce, broccoli and spinach into plots that we had treated with the 15 herbicides we evaluated. Four of them injured at least one of the  crops. These were 2,4-D choline (Embed), Dicamba (Enginia), Sujlfentrazone+Carfentrazone (Zeus) Carfentrazone (Aim,Shark). 

In terms of broad spectrum weed control with no soil activity, only two of the fifteen herbicides we evaluated were comparable to Glyohosate. It is likely that a combination of a grass and broadleaf herbicides will be necessary.

Area wide Insect Trapping Network   VegIPM Update, Vol. 15, No. 21, Oct 16, 2024

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

Corn earworm: CEW moth counts increased in most traps; about average for early October.

Beet armyworm: Trap counts increased in most areas last week, and about average for early October.

Cabbage looper: Cabbage looper trap counts still most locations, below average for this time of the season.

Diamondback moth: Adult activity increasing, particularly in the Yuma and Dome Valleys.  Above average for this time of season.

Whitefly: Adult movement increasing Tacna, Dome Valley and Yuma Valley; overall about average for early October.

Thrips: Thrips adult movement picking up in all areas, overall activity above average.

Aphids: Winged aphids beginning to show up the north Yuma and Gila Valleys; about average for early October.

Leaf miners: Adult activity light in all areas, about average for this time of season