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. 
 

 
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.

It is difficult to solve a problem without first identifying what is causing it. We recognize that helping people to identify problems is an important part of our jobs and we spend much of our time collecting and analyzing samples. Most of the samples that we receive are for either weed identification or herbicide injury evaluation.

Although there are probably less than 50 common weeds in this region, there are hundreds more that occasionally turn up. We have been identifying weeds for many years but there are few weeks that we don’t see one that we are not sure about. Even the common ones can look significantly different when they are growing in different areas under different conditions. Weeds growing in the irrigated desert can have characteristics that complicate their identification. Annual weeds are normally classified as those that live during the summer or winter and then die. This distinction is often inaccurate in the low deserts of Arizona when weeds that are normally classified as summer annual weeds survive into the winter months under mild winter temperatures and frequent irrigations. It is not uncommon for some summer annual weeds to live for two years as biennials or even longer as weak perennials. Similarly, winter annual weeds can sometimes survive through the summer where they are shaded by a crop and receive frequent irrigations. One of the best resources for identifying weeds is by Joe DiTomaso that is two volumes, 900 pages, contains more than 750 species and is only $80. Click on the next link for more information on Weeds of California and Other Western States.

We also receive many herbicide injury samples and these can be even more difficult to accurately identify. There are more than 100 different active ingredients contained in herbicides used in this region. None of these produces crop symptoms that can’t also be produced by many other factors such as diseases, insects or other pests, nutritional problems, environmental stresses etc. Sometimes symptoms, patterns in the field or herbicide use history make diagnosis easy although often the only conclusive method to identify the problem is chemical analysis. This can be costly and time consuming but we send many samples to laboratories every year.

Processing weed identification and herbicide injury samples are an important part of our responsibilities. You can download the sample ID form or fill it out at the Agriculture Center when you drop samples off. Please let either Barry Tickes or Marco Peña know that you are bringing samples by and we will arrange to receive them. We are currently working on locating a refrigerator for sample drop off when no one is around to receive them.