April 2013
When do I need to spray? That’s a question that comes my way often. How do I know the answer for your orchard? Biophenometers, traps, experience and knowledge of the entire region. Every year in February, I place biophenometers in Palisade, Olathe, Eckert, Paonia, Rogers’ Mesa and Cedaredge. A biophenometer is a self-contained device that works around the clock keeping track of temperature data. This data is used to track development of your favorite pests. I also have a network of pheremone traps for each pest, in each of these areas. Once I obtain a biofix (the start of continuous trapcatch) I will note the biophenometer reading and start accumulating degree days. Each pest has a phenology unique to it. The decision to spray along with the timing needs to be further refined by pest populations in your block, daily temps just prior to spraying and the choice of materials you plan to use. For example, if the population in your orchard is low, it may be advisable to delay a bit, or if you farm at the lowest elevation in your area you may want to be a few days early. As new materials become more pest specific and active on a particular life stage, timing becomes more critical. Every year I work at refining my pool of knowledge that I use to determine spray timings. I make notes of who suffers pest damage and why. Damage is not always the result of poor timing. It can be insufficient spray coverage or the wrong material.
Controlling any pest is a matter of:
1) Using the correct material properly. Choose a material that will do the job. Is resistance an issue? Use a high enough rate to do the job or change classes. Is it a special need and/or timing material? Does it need buffering or a spreader? Is storage temperature an issue?
2) Proper timing of your application. All pests have an optimum time to control them. Do you know that timing for each pest in your orchard?
3) Good coverage. Have you ever walked behind your sprayer and looked at your coverage, looked at all the dry areas in your tree? Water volume is not the issue! I’ve seen dry spots behind a 300 GPA application. According to Kevin Day, University CA farm advisor, “Excessive speed is probably the biggest roadblock to thorough spray coverage”. An air blast sprayer must move the “resident” air from inside the tree before it can replace it with the spray laden air. According to Day, “sprayers should never travel over two miles per hour.” I’ll bet that if I were to drive two mph in a race I would lose to every sprayer in the county!
During the bloom period your trees are at a point of maximum stress. The small spur leaves on apples feed the developing fruit until shoot extension and enough new leaves develop to take over. Strong spur leaves are critical to fruit set, fruit size, and fruit calcium at harvest. Final fruit size is determined immediately post bloom during the cell division stage. This is a great period to boost nitrogen levels with urea or calcium nitrate. It’s also a key time to increase calcium levels in your fruit. Don’t forget to feed your crop.
“Man despite his artistic pretentions, his sophistication, and many accomplishments, owes the fact of his existence to a six-inch layer of top soil – and the fact that it rains.” Anonymous
Codling moth flight generally begins in apples during bloom or shortly after (It started last week in Mesa county), so traps should be in place by bloom. If mating disruption is used for codling moth management, dispensers should also be in place before bloom. Every year traps go up and catch a few early moths, then cold weather arrives and traps remain empty for a while, then counts go back up with warmer conditions. Do the early counts justify setting a biofix and starting phenology models to estimate the best timing for insecticide applications? There is no single correct answer to this, but if traps captured more than a few moths (3 to 5 per trap in any block), mating and egg-laying likely occurred at levels that will generate at least some early infestations of fruit when larvae hatch from eggs beginning about 240 DD (base 50 F) after the initial captures. Preventing those infestations still requires that an insecticide residue be on fruit when larvae chew through the "skin" of small fruits before they begin tunneling toward the center. Several good insecticides can be used to protect fruit; they include older compounds where there are no resistance problems (Imidan, Intrepid, and others) and a number of new alternatives such as Altacor, Assail, Delegate, and Rimon.
Green peach aphid (GPA) has a host range of over 875 species of plants, including all stone fruits and many ornamental shrubs and vegetables. GPA has a complex life cycle with five distinct morphological forms (eggs, nymphs, winged females, winged males and wingless females) and two behavioral forms (flight and flightless). Eggs hatch in the spring, producing wingless females that reproduce parthenogenetically. (OK time to get the dictionary out!) It means without fertilization from males. These eggs develop so quickly that they hatch before they exit the female and living 1st instar females are born. After several generations of wingless females are produced, winged females are produced which migrate to secondary herbaceous host plants where they produce more wingless females by asexual reproduction. This event in the life cycle is part of what causes us to believe that the population has “crashed”, when in fact it has simply moved. Other factors leading to a mid-season population crash are, decline in plant nutritional quality, increased natural enemy pressure and extreme weather events such as severe rainstorms. Toward the end of summer, winged males and females are produced. They migrate back to their primary host plant (peach), mating occurs and over-wintering eggs are laid at the base of buds. These eggs are oblong 0.6mm x 0.3mm (smaller than the head of a pin) and shiny black. Temperature plays a principal role in GPA biology. The longevity of adults is 3 months at 41F and 10 days at 77F. Longevity of nymphs is 21 days at 50F and 7 days at 77F. Females are capable of producing as few as 36 offspring at 50F or as many as 76 offspring at 86F. Fertility drops rapidly at temperatures over 86F. GPA adults can withstand 32F and larvae will survive to the 4th instar at 37F.
There are two main reasons that aphids become a problem, nutritional status of the plant and their relationship with predators and parasites. Aphids feed on the sap of plants. Excessively vigorous trees with high levels of soluble nitrogen allow GPA to reproduce at faster cycles. When aphids disperse from crowded conditions they exhibit an orientation to lighter green, fast growing terminals with high N levels. Mature leaves with less nitrogen cause a decline in reproduction by at least 50%. Once terminal buds set, aphids will usually cease reproduction and leave within the week.
All general predators plus many specialized predators and parasites attack aphids. Many years these biological controls will keep populations in check. Weather is a primary factor in biological control. Aphids sit attached to their food source, it only takes a brief period of warmth to allow them to feed. On the other hand, predators need longer periods of warmth to search for their food, and find it before temperatures drop and they become too cold to function. The other key to predator population levels is the choice and timing of insecticides you use. I’ve witnessed the explosion of aphid populations when a broad- spectrum material was used at an improper timing.
With the addition of stone fruits to the Provado label, bailing yourself out of a GPA problem is easy if you’re a conventional grower. If GPA is running rampant in your organic peach block you’re in trouble! As with any pest, the best control timing is the over-wintering stage, as it emerges in the spring. A major factor in controlling GPA is proper timing and coverage of a dormant oil application. Keep an eye on eggs prior to bud swell in the spring. They’re most vulnerable to oil applications just before they hatch.
“Politics is the art of looking for trouble, finding it everywhere, diagnosing it incorrectly and applying the wrong remedies.” ― Groucho Marx
If you’re using Entrust as part of your pest control program you’ll notice a difference in the material this season. It’s now a liquid product, Entrust SC is a soluble concentrate. Here’s the conversion table.
Entrust WP Entrust SC
.50 oz = 1.6 oz
.75 oz = 2.4 oz
1.00 oz = 3.2 oz
Here’s a link to a great webpage that shows the impact various insecticides have on different beneficial’s.
http://enhancedbiocontrol.org/
As always! Please give me a call with any questions.
Larry
970-234-3424