Pyrethroid v/s Reduced Risk product usage for Hullsplit/May Spray

A few people have inquired about the differences between spray product choices for worm control during Hull Split and/or "May" Spray. I thought I would highlight some of the thoughts that the UC has developed over the years regarding this decision. Some of this may be redundant, but hopefully some new points will be brought to the table.

Which product is best?
Determining which product is the best treatment option for your orchard depends on budget, pest pressure, timing, and familiarity.

Pyrethroid products are effective in knocking down adult moths and killing larvae that come in contact with the product. Persistence of the product within the field is not as long as the reduced risk products (about 2-5 days less), but they are useful for later hullsplit applications - around 2-5% for optimal timing. The downside with pyrethroids is the assumed mite flare up, knock down of orchard beneficial insects, and water run-off issues. A miticide should be tank mixed with the hull-split application if applying a pyrethroid.

"Reduced risk" products (i.e. Entrust, Success, Delegate, Intrepid, Belt, etc.) target the eggs and larvae of the moths. They do not knock down adult populations as well as pyrethroids, but control developing larvae more effectively and selectively. These products tend to persist within the orchard a little longer, providing longer control and thus can be applied earlier than pyrethroid products (when blanks split). They have a minimal effect on beneficials, allowing the natural predators to help control mite populations, usually preventing a mite flare up, thus not requiring the tank mixing of a miticide.  These products are very effective but resistance to the mode of action may occur - so chemical class rotation is important if products are sprayed more than once per season. Water impacts appear to be minimal.

Currently, a pyrethroid treatment is cheaper than reduce-risk products - even including the cost of tank mixing the miticide. If the hull-split spray is delayed due to a spray rig breakdown, late start, etc, and the spray is beyond 5% hullsplit, a pyrethroid is the better product to use to help knock down adult populations. If sprays are being applied before the 2% hullsplit, a reduced risk product should be used.  Making use of both products can help increase the window of hull-split sprays. Tank mixing of reduced risk and pyrethroid products is not advised due to the cost and no additive gains in worm control.

Should I ever Spray a pyrethroid in the orchard?
Philosophically, most researchers/entomologists will say "no." Clearly, there are effective options out there for worm control that do not require the use of broad spectrums. It is important, however, to acknowledge that there are more orchard insect pests than moths/worms. Leaf-footed plant bug, stink bugs, and other insects may warrant a broad spectrum spray. In these years where the spray has to be made, it is important to develop a strategy to help re-balance the loss of natural predators within the orchard. The benefits of the reduced risk products are due to the selective nature of their chemistries; they have minimal impact on non-targeted insects and thus allow the orchard to gain a biological balance. 

May Spray: Its not just for PTB anymore. 
Reduced risk pesticides (i.e. Entrust, Success, Delegate, Intrepid, Belt, etc.) can be applied in May because they do not have the effect on mite predators like the broad spectrum chemistries (Pyrethroids, Organophosphates). For the past few decades, the UC has made a conscience effort to move away from May Spray timing of NOW and PTB due to the flare up potential of the broad spectrum chemistries. This has changed. A spray for NOW and PTB can be made without the expected mite flare up with reduced risk pesticides. This will help reduce the over wintering/first flight population of NOW within the orchard, possibly preventing a hull-split NOW treatment. This spray may be important for orchards with historically low populations, orchards with sub-par sanitation that need more effective NOW control strategies, or for pistachio and almond growers who have these respective crops in side-by-side plantings.

Remember: Pull those mid-July leaf samples

It is that time of year to pull Mid-July leaf samples. Please see last year's article regarding leaf sampling for more information.

Orchard Cover Cropping pt 1

Written by: Jessica Corcorran, Pomology Intern, UCCE Merced County

Jessica was selected by a committee to serve in the Summer Pomology Internship Program funded by the Almond Board of California. Being assigned within Merced County, she is working on several research projects, attending farm calls, and getting a feel for what it takes to be an extension agent. It is our hope that her career path will lead to extension work, hopefully serving the almond industry within California. She is entering her Senior Year at Cal Poly.

The use of orchard cover crops is not a new practice. The benefits of cover crops have long been recognized and have been widely used in agriculture. In recent years, cover crop use has increased due to a multitude of reasons which include soils health improvement, increased soil fertility, and increased water retention and penetration. In today’s post, I will cover the impacts of cover cropping on soil health. In subsequent posts, I will discuss other benefits of cover cropping, general pros and cons, as well as the practicalities of implementing a cover crop in an orchard.

Cover crops have the ability to greatly improve soil quality and structure. Water penetration is often compromised by soil compaction in orchard soils.  The roots of the cover crop and their ability to move through the soil can help to reduce soil compaction by tillage and harvesting equipment.  Plow pans have even shown to be corrected by the use of cover crops. The fibrous roots of the cover crop also help to stabilize soil aggregates, which improve soil structure and aids in effective water infiltration. The addition of organic matter in the soil invites beneficial microorganisms. During the breakdown of organic matter, indigestible compounds are formed that are resistant to decomposition. These compounds bind soil particles to form soil aggregates. Soil aggregates are important for improving water holding capacity and aeration.

Organic matter is often lacking in perennial agriculture systems. Typically, only through leaf abscission in the fall is organic matter returned to the soil. Cover crops can serve as “green manure”, meaning the plant matter is returned to the soil through tilling. This increases the amount of organic matter within the area tilled and the subsequent nutrient holding capacity of the soil zone. These nutrients will be available for later use by the trees. If a leguminous cover crop is used, nitrogen is naturally fixed in the soil and can reduce the amount of nitrogen fertilizer needed. Purple vetch or Lana vetch, for example, is shown to add 100 to 200 pounds of nitrogen per acre once it is tilled.  The presence of microorganisms and earth worms is largely dependent on the amount of organic matter in the soil. By using a cover crop and building organic matter, increased population and activity of beneficial microorganisms and earth worms is often observed. Benefits of these organisms include soil buffering capacity, nutrient holding capacity, water infiltration, and soil aggregation.

Soil that is free of or lacking plant cover is very susceptible to soil erosion. The preservation and longevity of soil fertility is increased with the use of a cover crop. In the central valley, dust can be a problem, especially during periods of high wind and at harvest time. Implementing a cover crop reduces the soil’s exposure to wind and disruption by harvesting equipment. By not leaving the soil surface exposed, the occurrence of soil crusting and water runoff is also greatly reduced. 

2010 Hull Split time...

I feel that the majority of topics regarding hull split have been discussed in prior entries, so I thought I would briefly make a few points of considerations for 2010:

1). Navel Orange Worm (NOW)/ Peach Twig Borer (PTB): Both insects cause damage to almonds, often NOW damage hiding PTB damage. Both insects are susceptible to the same insecticides. The 2010 treatment window for the 2nd flight of PTB will be overlapping with hullsplit. This is good because we can make one spray for NOW and PTB. This is bad because in years were the 2nd PTB flight occurred during hullsplit, worm damage was higher.  If no PTB treatments have been made and no NOW/PTB treatments are scheduled, I would plan to make one within the coming week. Reduced risk products or pyrethroids will provide control for both worms. Related topics previously covered: Peach Twig Borer, Navel orange worm, and hull split insect management.

2). Apply pesticides slowly - do not exceed 2 MPH with spray rigs.

3). Hull rot: Hopefully nitrogen applications have ended. Plan to reduce water to 80% ET for the coming two weeks. By the last week of July, first week of august, resume full ET. This will help reduce hull rot. Please see the previous article on hull rot.

4). Mites: Haven't been much of a problem this year, but keep in mind that the use of a pyrethroid at hullsplit will most likely cause a mite flare up by harvest. A miticide should also be applied at hullsplit if a pyrethroid is used. There are a few products available that can knock down high populations of spider mites should a flair up occur. It is critical that these products are applied before webbing appears.

5). Harvest: Hullsplit appears to be a week later this year, suggesting that harvest will be at least a week late as well. Keep trees well watered through August so that stress is minimized when the harvest dry down occurs. Harvesting one week later also means a shortened post harvest period, reducing the time to perform post-harvest tasks.

Hope this helps!

2010 NASS Almond Objective Forecast

As reported July 8th, 2010, from the USDA National Ag Statistics Service:

"2010 CALIFORNIA ALMOND FORECAST UP

California's 2010 almond production is forecast at 1.65 billion meat pounds, up 8 percent from May's subjective forecast and 17 percent above last year's crop. The forecast is based on 740 thousand bearing acres. Production for the Nonpareil variety is forecast at 640 million meat pounds, 18 percent above last year’s deliveries. The Nonpareil variety represents 39 percent of California’s total almond production.

Despite a variable spring, weather in 2010 had few negative effects on the coming almond crop. Bee activity was reported to have been hampered some by the rain, but overlap of varieties was excellent. Nut sets were higher than in 2009; nut weights and measurements were up as well. High winds resulted in some nut and tree losses, but damage was not significant. Wet weather increased concerns about fungal infections and rot, but additional sprays have kept the problem in check. A benefit of the cool weather has been low insect pressure; overall, the trees are growing well and the crop is developing in good condition.

The average nut set per tree is 5,956, up 7 percent from 2009. The Nonpareil average nut set of 5,583 is up 9 percent from last year’s set. The average kernel weight for all varieties sampled was 1.72 grams, 9 percent above last year. A total 98.7 percent of all nuts sized were sound."


The full report can be found here.

Unusual Leaf Symptoms in 2010- Some thoughts...

Several calls have been coming in over the past few weeks regarding unusual leaf symptoms on almonds. For the most part, the symptoms have appeared across varieties, but with one variety being more heavily affected within a single orchard. Symptoms also have appeared in waves, starting about mid-April, again in May, and then again in June. Orchards all over the San Joaquin Valley have been calling in with reports, varying in ages, varieties, nutritional status, and orchard spray practices.

The symptoms appear to start off as small, yellow pin-head sized lesions on the leaf (Figure 1). Following a few days of heat, the lesions enlarge, and become necrotic, often abscissing from the leaf (Figure 2). The margins of the leaf appear to be the most severely affected, with some damage evident throughout the leaf blade.

Figure 1: Initial damage observed of foliar problem commonly experienced in the 2010 crop year. Photo provided by Allan James, Mid Valley Ag.

Figure 2: Damage to almond leaves experienced in the spring of the 2010 growing season. These symptoms appeared later than the symptoms observed in Figure 1, usually after a hot spell.

I initially thought that the problem was due to foliar nutrient sprays - either due to contaminated products or cation activation (iron, zinc, manganese, magnesium, etc.) by a rain event. This didnt seem to fit the symptoms in every orchard due to some orchard owners not spraying foliar nutrients.

Symptoms also appeared similar to potassium deficiency, but the widespread occurrence throughout the valley does not support a nutrient deficiency.

The possibility of corky spot was brought up, especially since the leaf symptoms look similar to the pictures of this disease. Corky spot is an unknown disorder that tends to be associated with nonpareil planted on seedling almond type rootstock (i.e. bitter almond). Due to the widespread occurrence of this symptom across differing orchard ages, nursery sources, and rootstocks, I doubt that this is a case of corky spot.

I also was concerned about some type of foliage disease due to the spread of the disease and season progression. Samples were sent to UC Plant pathologists and they were unable to isolate any disease causing agents. Inconsistent isolation of various fungi from different samples led to the conclusion that the disease was not due to a fungal pathogen.

Through discussion with other advisors across the state led to the possibility of Peach Silver Mite (PSM), a mite of the Eriophyid mite family. Damage observed from previous years in Sacramento valley appears to be similar to the damage observed this year. PSM feeding and population growth occurs during cooler temperatures. Upon hot temperatures, the mite basically disappears from the orchard.  PSM are quite small, need a 15x or stronger hand lens to see, and are controlled by most miticides, oil, and even sulfur. Observations by UCCE advisor Franz Niederholzer in Yuba/Sutter Counties indicate that they are not controlled by Acramite.

Experience from other advisors suggest that this damage is due to PSM or some other mite within the Eriophyid family. This year, many people applied miticides later due to the cooler temperatures and reduced pressure. This may have allowed the populations enough time to build to high levels within the orchard and cause the observed damage. Damage that is appearing now most likely occurred a few weeks ago. For the most part, there is nothing for the grower to do at this point since the damage already occurred. I don't think, unless we have another cool year, that these symptoms should appear next year.