TM
Tree nut growers have battled to control pests and diseases like navel orangeworm, peach twig borer and rust for many years to protect crop yields and quality. The list of serious pests and diseases is a little longer these days and presents a new round of challenges.
The Almond Board of California presented a series of workshops this spring to bring growers and pest control advisors up to speed on new pest challenges,
a new disease and control measures to keep their trees productive and healthy.
Vertebrate Pests Cause Orchard Damage
It’s not just insects that need to be controlled in orchards.
Julie Finzel, UCCE natural resources advisor in Kern County, noted orchard damage to crops, trees and irrigation systems is occurring.
Ground squirrels, gophers and rats are the main culprits, but damage, particularly to irrigation systems, has been blamed on coyotes and, in some areas, feral pigs.
Identifying the culprit species and choosing the most effective control method and timing are critical for cutting down on vertebrate pest populations.
Fumigation, baiting and trapping are control measures for ground squirrels. Finzel said matching their activity with the method will provide the most success. For example, baiting in the spring when there is plenty of green foliage will not be successful. Fumigation works best in the spring when soils are moist.
Strategies for pocket gophers include habitat modification, baiting, burrow fumigation and trapping. Fumigation with aluminum phosphide is allowed, but applicators must have a license to use it.
Aggressive mummy sanitation is currently the most effective management strategy.
— Mahesh Ghimire on controlling Carpophilus truncatus
Roof rats have caused major damage in almond orchards, burrowing at the base of trees and eating kernels. Elevated bait stations placed up in the trees eliminated access to bait for non-target species. The Almond Board of California is currently supplying these bait stations for growers.
Wild pigs can be a problem in orchards adjacent to open rangelands. Finzel said populations of this non-native species are growing and they can carry diseases.
There is little chance they can be eradicated, and Finzel noted that 70% of the population must be removed annually to keep them under control. Control options include exclusion, hunting and trapping. No toxic baits are allowed.
Crows, geese, starlings, magpies and scrub jays are also listed as orchard pests. Only crows, magpies and starlings can be taken without a permit.
New Fungal Disease
Red leaf blotch is a new invasive disease in almond orchards and was first detected in California only two years ago.
Mohammad Yaghmour, UCCE orchard systems specialist in Kern County, said new disease emergence is likely the result of several factors, including reduced fungicide applications in orchards and movement of plant material into California.
Red leaf blotch is a fungal disease that affects the leaves. The pathogen, Polystigma amygdalinum, is dependent on living plant tissue for growth, reproduction and feeding and cannot be grown on a culture medium.
Infected leaves have visible yellow blotches at first, then red blotches. The leaves become necrotic and drop early, depriving trees of photosynthetic activity and carbohydrates needed to fuel the following year’s crop.
Leaves on the ground will serve as inoculum for the next growing season.
Yaghmour said symptoms of infection begin to appear as small pale yellow spots on leaf surfaces. As the infection progresses, the spots become larger, turning orange or reddish-brown. The blotches eventually cause leaf drop.
A preventative fungicide strategy includes a three-spray program, with the first timed at petal fall. A second spray is timed two to three weeks later and a third spray five to six weeks after petal fall. These sprays also help manage other spring diseases, including shot hole, rust, anthracnose and scab. Fungicides applied during bloom and after symptoms are visible are not effective.
Effective fungicides are FRAC groups 3+7, 3+11, 7+11, 7+12 and FRAC 3 triazoles. Examples are fluopyram + trifloxystrobin, pyraclostrobin + boscalid, difenoconazole + pydiflumetofen and flutriafol. Yaghmour noted that it is important to rotate modes of action to prevent resistance.
Cultural practices can help mitigate this disease. They include removing leaf litter from the orchard floor, applying urea or lime sulfur to accelerate leaf decomposition and biosanitation using beneficial microbes. These strategies, Yaghmour noted, are only effective when applied over a wide area.
Hemipteran Pests
The most common hemipteran pests affecting almond crops are leaffooted bug, brown marmorated stink bug and green stink bug. Depending on the timing of feeding, these large bugs can cause nut drop and brown spot on kernels.
Mahesh Ghimire, UCCE assistant research specialist in Stanislaus County, said factors associated with crop damage are insect size and feeding damage, population abundance, feeding timing and surrounding landscape.
Temperature also matters.
Insect growth and development are related to temperature, and feeding activities can increase due to higher metabolic activity.
Ghimire cited a study done in Japan that noted a warm winter favors survival of overwintering stink bugs.
There has been increased plant bug and stink bug activity and crop damage in recent years.
Testing trap and lure combinations for leaffooted bug is underway. Clear panel traps, pyramid traps and experimental vibrational traps, all baited for brown marmorated stink bug, are also being tested. Ghimire noted that the first brown marmorated stink bug capture was March 3.
A trial of insecticide efficacy of biological and reduced-risk materials showed no treatments were statistically different from each other.
Sap Beetle Continues to Spread
The most recent invasive pest, the sap beetle Carpophilus truncatus, continues to spread in San Joaquin Valley tree nut orchards.
Identification of the pest and damage is important, as other sap beetle species look similar.
Ghimire said C. truncatus has multiple generations and can be active on mummy nuts on the ground throughout the season.
This pest attacks nuts at hull split and can cause significant damage.
Insecticide efficacy remains unclear and requires further research.
Aggressive mummy sanitation is currently the most effective management strategy for C. truncatus, Ghimire stressed. Sanitation must include complete destruction of mummies. Discing or burying nuts does not help. In a study, percent of nut damage by C. truncatus at harvest in double-pass sanitation showed a flail mower reducing damage from 3% with no sanitation to nearly 2%. Sanitation with the “mummy muncher” reduced damage to less than 1%.
Publisher’s Take
The Big Picture: What to do Next
1. Aggressive mummy sanitation remains critical for sap beetle control
Research presented at the workshop showed complete destruction of mummy nuts remains the most effective management strategy for Carpophilus truncatus.
2. Red leaf blotch requires preventative fungicide applications
Fungicides applied after symptoms appear are not effective. Timing applications beginning at petal fall is critical for disease management.
3. Vertebrate pest management depends on timing and species identification
Matching baiting, fumigation or trapping strategies to pest behavior improves control success and reduces unnecessary treatments.
4. Resistance management and mode-of-action rotation remain essential
Researchers stressed rotating fungicide and insecticide chemistries to help prevent resistance development.
5. Warmer winters may increase stink bug pressure
Studies discussed at the workshop noted mild winter temperatures can improve overwintering survival of stink bug populations.
Cecilia Parsons | Associate Editor
Cecilia Parsons has lived in the Central Valley community of Ducor since 1976, covering agriculture for numerous agricultural publications over the years. She has found and nurtured many wonderful and helpful contacts in the ag community, including the UCCE advisors, allowing for news coverage that focuses on the basics of food production.
She is always on the search for new ag topics that can help growers and processors in the San Joaquin Valley improve their bottom line.
In her free time, Cecilia rides her horse, Holly in ranch versatility shows and raises registered Shetland sheep which she exhibits at county and state fairs during the summer.