IN YOUR ORCHARD
TIME TO CONSIDER
Welcome to our new “Time to Consider” contributor, Dr. Brent Holtz! About Dr. Holtz: Dr. Brent Holtz has been an Orchard Systems Advisor for the University of California for 28 years, starting in Madera and currently in San Joaquin County. He and his family farmed almonds on their ranches in Modesto and Oakdale. Brent’s parents and grandparents were Blue Diamond Growers. Holtz attended Modesto Junior College, California Polytechnic State University, San Luis Obispo (B.S.), and earned both M.S. and Ph.D. degrees in Plant Pathology from the University of California, Berkeley. His research and education programs are focused on growing almonds in a sustainable manner in the San Joaquin Valley of California. Holtz is currently leading a research effort on whole orchard recycling where removed orchards are ground-up and incorporated into the soil to increase soil organic matter and soil water holding capacity.
Almond Bloom Diseases Almond trees are susceptible to blossom and foliar diseases when it rains at bloom time. Many of these diseases can be effectively managed with the use of properly timed fungicides. The decision, however, of when to spray and what fungicide to use can be quite difficult. The Central Valley typically receives a low amount of precipitation, but in many cases, we cannot predict when and how much it will rain. We often receive rain during the bloom period that can result in favorable conditions for several plant pathogenic fungi that can cause several diseases of almond blossoms. The fungi that cause these diseases are usually present in almond orchards, at higher or lower inoculum levels depending on the previous year’s disease incidence and current environmental conditions. Generally, a good disease management program is based upon a wise choice of fungicides and good timing and coverage. Growers should assess the diseases present in their orchards and select materials carefully. Not all fungicides are equally effective against all diseases. It is good to use more than one kind of fungicide to obtain a broader spectrum of activity. See the on-line publication “Fungicide efficacy and timing for deciduous tree fruit and
nut crops and grapevines” found at the UC IPM website at ipm.ucanr.edu/PDF/PMG/fungicideefficacytiming.pdf. This is the “Bible” of bloom and foliar disease management. Group numbers have been assigned to each fungicide based on its mode of action by the Fungicide Resistance Action Committee (FRAC) (www.frac.info/). Fungicides with a different group number are suitable to alternate in a resistance management program. Resistance to fungicides can develop over time with repeated use of any on FRAC Group, thus, we need to rotate the fungicides we use. When making fungicide applications, keep track of their FRAC numbers; and, if possible, make only one application of each of FRAC numbers 1, 3, 7, 9, 11, and 17 per season. After using one of these fungicides, rotate to another number, don’t use the same number for two consecutive sprays but be sure the fungicide selected has activity against the disease. For fungicides with other FRAC numbers, make no more than two consecutive applications before rotating to a fungicide with a different FRAC number. Under low rainfall forecasts, a single, delayed-bloom application of a newer pre-mixture fungicide such as a FRAC Group 3/11, 3/7, 3/9, or 7/11 will provide “reach back” and protection. A delayed bloom application is
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A L M O N D F A C T S
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