With last year’s unusually dry weather continuing into 2014, water running through irrigation systems has been a common sight in the dormant almond orchards of Sutter and Yuba Counties as winter has progressed.
In at least one irrigation district, growers irrigated with surface water into November before water deliveries ended for the season. Elsewhere, others began turning on their well pumps.
By mid-January, forecasts offered little hope for any significant rainfall in the short term. Meanwhile, availability of surface water for the upcoming season is in serious doubt.
“Growers are very, very nervous that they may have little or no surface water this year,” says Franz Niederholzer, University of California Cooperative Extension farm advisor for Colusa, Sutter and Yuba Counties.
On the plus side, temperatures, aided by the early December cold spell, have been cold enough to provide almond trees the number of chilling hours needed for normal development of flowers and leaf buds, he reports.
Typically, the early-pollinating varieties in this area start blooming in the first half of February. However, warmer temperatures, like those in the first part of January, could result in an earlier bloom, Niederholzer notes.
To prepare orchards for the start of this year’s bloom, he offers these tips.
Clean up the orchard floor
The taller the vegetation and the drier the grounds, the less frost protection for the tree wood and buds. That’s why he recommends mowing and irrigating the orchards prior to bloom, especially if there has been no rain to little rain and the soil is dry. “Moist, bare soils absorb heat from the sun during the day and radiate it back to the air at night,” he says. “University of California research shows these conditions can add a least one degree of warmth to the air temperature in an orchard compared to tall vegetation and dry ground. If weather remains dry and warm days push earlier bloom, the lack of humidity may translate to low dew points at night or early morning that could mean colder mornings than average.”
Check out your irrigation system
If you haven’t already been irrigating this winter, now is the time to make sure there are no surprises when you turn on the water for the first time this season – assuming you have water to use. Check for worn nozzles or emitters, clogged filters and emitters, misadjusted pressure regulators and leaks, including damage from coyotes, ground squirrels, ATVs and the like. For more information on maintaining a micro-irrigation system, see the UC publication Maintaining Microirrigation Systems. It can be ordered online at: http://anrcatalog.ucdavis.edu/Irrigation/21637.aspx 
Every drop counts
Make every drop count
Prospects of a water-short year heightens the need to use irrigation water as efficiently as possible.
“If you haven’t already done so, this is great year to adopt technology, like soil moisture sensors and pressure bombs, for monitoring soil or tree moisture levels and scheduling irrigations at the most effective times,” Niederholzer says. “Take steps now to determine what equipment you’ll need and how to get it in place before your trees start pulling water at bloom.”
Wet your soils before bloom
The roots of almond trees begin growing about four to six weeks before bloom. That’s why, if orchards don’t receive enough rainfall this winter to wet the root zone by the middle of February and water is available, Niederholzer advises irrigating ahead of bloom. “Make sure that as much of the root zone that your irrigation system can reach has adequate water,” he says. “Monitor soil moisture to a depth of at least 3 feet and preferably to 4 feet during irrigation. Don’t apply excessive water ahead of bloom, because the trees are not using any and tree roots may be damaged by too much water. Moist soil with no or very short vegetative cover results in a warmer orchard than dry ground.”
Prepare sprayers for bloom fungicide applications
Wet weather during bloom sets the stage for fungal diseases, including brown rot and anthracnose during the earlier part of bloom and gray mold and shot hole later in the bloom.
Lack of rain during bloom doesn’t necessarily eliminate such threats. For example, dew on the flowers can provide enough moisture to allow brown rot infection, Niederholzer notes.
Under wet weather conditions, University of California guidelines call for applying fungicides once at the pink bud stage and again at full bloom. Studies by Jim Adaskaveg, University of California, Riverside, have found that a single fungicide spray in between those two times can protect almond trees from bloom-time fungal diseases when bloom weather is dry.
Keep the bees safe
In addition to locating where you’ll put your bees hives for pollinating your trees, he recommends following appropriate practices to protect bees from bloom sprays. That includes applying only fungicides during bloom, Niederholzer says.
“The purpose of spraying almonds at bloom is to control fungal diseases and most fungicides don’t appear to pose a threat to the brood,” he says. “There’s no compelling reason to spray the trees with other materials at this time of the season, especially since we don’t know the impact of combining fungicides with pesticides, nutrient sprays and/or adjuvants on bees and hive health. Besides, if you’re getting good coverage of the entire tree, you don’t need to use adjuvants to improve coverage – particularly at bloom. You can apply pesticides and nutrients later in the season after hives have been removed from the orchard.”
What’s more, when applied during bloom, fungicides should be sprayed late in the day or at night when bees have stripped the flowers of pollen for the day. Niederholzer notes. Not only will that reduce exposure of bees to the fungicides, but it can also prevent destruction of the pollen.
“Pollen grains have to be become hydrated as part of the germination process,” he explains. “But, spraying them with water can cause them to over-hydrate and fail to grow. If there is good bee activity in the orchard, the foraging bees will have picked up all the available pollen produced that day by mid-afternoon. So, by waiting until the late afternoon to spray fungicides, you help protect both the bees and the pollen.”
More from Western Farm Press