It’s been a warm winter and bud development on early blooming varieties was progressing in early January. This could mean an early bloom (with greater chances for frost damage) and early pest biofixes.
Consider honeybee health and safety when applying fungicides during bloom. UC fungicide trials and tables showing effective control are conducted with nothing in the tank at bloom but fungicide (no surfactant unless the label specifically calls for it). Time sprays after pollen has been stripped from the flowers (late afternoon through the night).
For bee BMPs, see: sacvalleyorchards.com/almonds/pollination/honey-bee-safety-during-bloom-2/
Frost protection: If freezing temperatures are forecast, turn on sprinklers when the wet bulb, not the dry bulb, temperature up wind of the orchard approaches the critical damage temperature. Don’t turn water off until the wet bulb temperature upwind of the orchard is above the critical damage temperature (or all the ice has melted). If rainfall has not been sufficient to wet the top foot of soil, run irrigation water a couple of days before expected frost risk— if water is available. If the top foot is moist but the surface has a dry crust, run water to moisten the surface so heat can be stored during the day prior to frost.
A moist soil surface will absorb more heat during the day – and release the heat at night – than if it is dry. Drip irrigation doesn’t provide much frost protection during a cold event, but can help if it is used to wet the soil surface ahead of cold – for example, early in the day before cold weather is forecast.
Flood irrigation can provide frost protection as long as the flow is sufficient to prevent the water surface from freezing during the frost event. If insufficient water is available to run water during the freeze, wetting the soil in advance will allow the soil to store more heat during the day to keep the orchard warmer at night.
If peach twig borer (PTB) was a problem in last years’ harvest, B.t. (Dipel, Javelin, etc.) sprays will provide control with minimal impact on honeybees. Spraying any other insecticide than B.t. at bloom risks hive health. Thresholds and treatment timings are available here: http://ipm.ucdavis.edu/PMG/r3300211.html.
PTB can also be controlled with a May spray or at hull split, so bloom insecticide is not essential to controlling this pest (see article on PTB in this newsletter).
Brown rot occurs with warm, wet (dew, rain, or fog) weather.
Flowers are susceptible from pink bud until petal fall, but are most susceptible when fully open. Management differs depending on rainfall. Guidelines are available here: ipm.ucdavis.edu/PMG/r3100111.html Anthracnose management in orchards with a history of anthracnose, or if weather is warm and rainy during bloom, begins with bloom treatments. Photos and management guidelines are here: ipm.ucdavis.edu/PMG/r3101111.html
Green fruit rot is caused by several organisms and can be a problem, especially during wet bloom seasons. Management guidelines can be found at: ipm.ucanr.edu/PMG/r3101711.html.
Bacterial spot can be reduced to low levels with a single full bloom or petal fall application of copper + Manzate timed ahead of warm, wet weather. If warm, wet weather persists, use low or a reduction in the rate of copper with each subsequent application to reduce the risk of leaf phytotoxicity. This disease, which overwinters in mummies and infested peduncles, can be a significant problem in Fritz, but present also in Nonpareil, Butte, Carmel and Price varieties. Management guidelines can be found at: ipm.ucanr.edu/PMG/r3101911.html
If scab or rust was a problem last season and inoculum is present in your orchard, monitor scab twig lesions for scab sporulation and leaves on new shoots for the presence of rust. Treat as soon as observed but prior to the next rain. Scab twig lesions typically sporulate in April. Dormant applications of chlorothalonil copper + oil may delay sporulation on scab twig lesions until after rainfall ceases thus avoiding the need to treat. Five weeks after petal fall is often an optimum timing for control of rust and scab. Control measures can be found at the following links.
- Scab: http://ipm.ucdavis.edu/PMG/r3100411.html
- Rust: http://ipm.ucdavis.edu/PMG/r3100711.html
Hang San Jose scale pheromone traps by the end of February to track male scale activity and relative amounts of beneficial wasps. See details and photos at: http://ipm.ucanr.edu/PMG/r3300811.html
Hang navel orangeworm (NOW) traps no later than mid-March. Pheromone traps track adult male flight activity, egg traps track egg-laying activity (most useful in establishing a biofix, ipm.ucanr.edu/PMG/C003/m003bceggtrapsnvl.html), and kairomone (bait-bag) traps track flight activity of gravid (egg-laying) adult females. See article in this newsletter on NOW control considerations for info on egg trap biofix in the Sacramento Valley.
Hang peach twig borer pheromone traps by March 15 for monitoring populations and to help with spray timing. Info at: http://ipm.ucanr.edu/PMG/r3300211.html. Start planning your nitrogen and potassium budgets for the upcoming season. Nitrogen management tools based on UC research are available at sustainablealmondgrowing.org. Approximately 20% of the year’s predicted nitrogen needs should be applied in late February or March.
Start planning your nitrogen and potassium budgets for the upcoming season. Nitrogen management tools based on UC research are available at sustainablealmondgrowing.org. Approximately 20% of the year’s predicted nitrogen needs should be applied in late February or March.