May 5, 2021Summer Sanitation Is Important as Ever
To contact John Palumbo go to: jpalumbo@ag.Arizona.edu
Herbicide resistant weeds have received a lot of attention in recent years. It is often misunderstood. Three of the most misunderstood concepts regarding herbicide resistance are: 1- Weed tolerance and weed selection are not resistance,2- Weed resistance is not universal and does not affect every weed of a certain species from field to field or within a field and weed resistance often takes much longer than insect resistance that is more common and occurs faster.
No Herbicide controls all weeds. Those weeds that are not controlled are tolerant. They never were controlled by that particular herbicide and they are often selected for and become more prevalent over time if the same herbicide is used. Resistant weeds, on the other hand, were controlled at one time by a particular herbicide and have naturally developed a trait that stops the herbicide from working. These resistant weeds survive from generation to generation and become more prevalent over time.
Weed resistance does not occur in all weeds in a field at the same time. It can be just one plant of trillions in a field. As this plant survives the herbicide and goes to seed it becomes more widespread in the field and in other fields. We conducted a trial in Parker last year where sprangletop survived Glyphosate in one field and was killed by the same treatment down the road. If your neighbor has resistant weeds it doesn’t mean that you do too.
Lastly, insect resistance to insecticides has occurred in this region for many years and was the first exposure that many pest control advisers and growers had to pesticide resistance. The principals are the same although insects generally produce multiple generations per season and mutations that facilitate resistance occur faster than for weeds. Annual weeds often produce only one or two generations per season and resistance takes much longer.
It is that time of the year! Every year, September starts with “Is it April yet?” If you did not say that, then you cannot sit with us!
This past growing season has been an interesting one. From wearing masks at 120 degree to maintaining social distancing; while producing same amount of produce, feeding same amount of people, and dealing with same amount of disease and pests. A big thank you to everyone involved in agriculture for your hard work and perseverance.
In regards to plant health, we had plenty of disease problems to deal with this year. Below is brief report of the major diseases observed in growing season 2020/2021 and the disease we should be keeping an eye on for next growing season.
We observed a lot of fields with fusarium wilt this year. We had a lot of infected watermelon fields from Winterhaven to Yuma, Wellton, and Mohawk Valley. Rain, and overwatering of fields when plants set fruits might have contributed to the disease development.
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.
Fusarium wilt of Lettuce
Though detected in a lot of fields and some new fields, the disease pressure in lettuce was relatively low. Please continue with proper management practice for next growing season. Avoid overwatering, add soil amendments/organic matter, practice crop rotation if possible.
Lettuce dieback associated virus
Lettuce dieback is a soil-borne disease caused by two closely related viruses from the family Tombusviridae Tomato Bushy Stunt Virus (TBSV) and Lettuce Necrotic Stunt Virus (LNSV) that has been reclassified as Moroccan Pepper Virus (MPV). The disease has been observed throughout the main lettuce producing areas of California and Arizona.
Sclerotinia rot (known as lettuce drop) is caused by fungi Sclerotinia sclerotiorum and Sclerotinia minor.The initial aboveground symptom is observed as wilting of outermost layer of leaves giving an impression of stress in plants. However, as infection progresses rapidly towards other leaf layers and the entire plant wilts including the head. The entire plant/planting can collapse within the matter of 2 days when the condition is favorable. Management practices include use of subsurface drip irrigation, keeping the top 5-8cm of soil on planting bed is crucial. Deep plowing, crop rotation with non-hosts like small grains and broccoli, removal of infected plant tissue from the field etc. help reduce the inoculum level. Soil fumigation is effective though may not be economical. In Florida growers flood fallow their lettuce field for 4-6 weeks in summer which has almost 100% control of S. sclerotiorum. This is something you might wan to consider doing this summer if you have had high disease pressure in your fields this growing season.
Downy mildew has been a problem for years in lettuce as well as spinach. One of the main reason that hinders the disease management is the complexity of the pathogen. Bremia lactucae (lettuce pathogen) consists of multiple races (pathotypes), and new races continue to occur as pathogen evolves. The pathogen is one of the fastest evolving plant pathogen. And each pathotypes have developed insensitivity to fungicides to different extent. Resistant cultivar, preventative application of fungicides are effective to some extent. Reducing leaf wetness and humidity by using drip or furrow irrigation can be helpful.
Impatiens necrotic spot virus (INSV)
INSV has been detected in a number in fields mostly in Tacna/Roll/Wellton area. It has been found in lower numbers in Gila Valley. If your field has been infected with INSV this growing season, be proactive next season in regards to clearing up the weeds, managing thrip population etc. If you see symptomatic plants please let me or Dr. Palumbo know.
This week in Clinic
If you haven’t submitted your entry for Melon powdery mildew fungicide trial for this spring please send it to Dr. Bindu Poudel-Ward (email@example.com)
Two years ago, Alphabet’s (Google) X-Labs initiated one of their infamous and far reaching “moonshot” projects focused on growing food sustainably on global scale. As you might expect, the project has been, and is kept pretty secret, but the company recently unveiled some details about the project through a company blog article (Grant, 2020) and their newly established website (https://x.company/projects/mineral/). The project is called “Mineral” and according to project lead Elliot Grant, the team has been working “alongside experts in the field – literally and figuratively…developing and testing a range of software and hardware prototypes based on breakthroughs in artificial intelligence, simulation, sensors, robotics and more”.
One of the tools the team has developed is a self-propelled “plant buggy” equipped with multiple cameras, sensors, GPS and other electronic equipment (Fig. 1). According to Mineral’s website, “Over the past few years, the plant buggy has trundled through strawberry fields in California and soybean fields in Illinois, gathering high quality images of each plant and counting and classifying every berry and every bean. To date, the team has analyzed a range of crops like melons, berries, lettuce, oilseeds, oats and barley—from sprout to harvest.” Stated objectives of Mineral’s software are to combine and analyze data collected from the field, soil health information and weather data to 1) predict how different varieties of plants respond to their environments, 2) allow growers to treat individual plants with fertilizers and pesticides to optimize production and reduce inputs and 3) help growers predict the size and yield of their crops.
It is exciting that a cutting-edge tech company like Alphabet is taking on an agricultural project like this. It will be fascinating to see what technical breakthroughs and solutions the company will be able to achieve for all crops, including vegetables.
Grant, E. 2020. Mineral: Bringing the era of computational agriculture to life. X Development LLC blog article. Mountain View, CA: X Development LLC. Available at https://blog.x.company/mineral-bringing-the-era-of-computational-agriculture-to-life-427bca6bd56a.
The Yuma County Leaf Wetness Network remains in place for the 2018/19 vegetable season. Growers and PCAs may access information generated by the network by entering the following internet address: http://126.96.36.199:460
Upon entering the address above, you will be transferred to internet page that provides a series of tabs at the top of the page. Simply click on the tabs to access the information of interest.