Pest, disease and weed management options for tree nut growers as well as some helpful irrigation advice were shared with growers, consultants and industry professionals at the South Valley Conference hosted by JCS Marketing Inc.

Methods for control and preventing spread of the invasive weed silverleaf nightshade were presented by UCCE Restoration Ecology and Weed Science Advisor Mandeep Riar.

Silverleaf nightshade’s competitiveness and adaptability to different soils makes it difficult to control in young orchards. It’s reproduction by root fragments makes it difficult to control with tillage, which can spread the fragments throughout the orchard. Riar said trials have shown combinations of systemic and contact herbicides are needed to control the weed. Materials that showed the greatest efficacy in control were a combination of Venus and Rely and Crop Oil Concentrate applied when weeds were less than 6 inches tall, achieving 90%+ control at 28 days after application. Rely 280 application at 1 foot and greater had near 90% control at 28 days after application.

Red Leaf Blotch

The emerging fungal disease red leaf blotch (RLB) poses serious concerns for almond growers. Florent Trouillas, UCCE plant pathologist, said this disease, found for the first time in California almond orchards earlier this year, affects the leaves and can cause severe defoliation. All the most planted almond cultivars are susceptible to RLB, Trouillas said. Yellow spots on the leaves are early symptoms of an infections. Those spots enlarge and darken in May and June. Infected trees can defoliate as early as August.

RLB, which is widespread in Spain, is believed to have been introduced here by infected plant material. Reduction in the number of fungicide sprays in orchards may have led to spread of RLB in northern San Joaquin Valley counties and lower Sacramento Valley counties.

Chemical control with fungicides can be effective, but timing is important. Fungicides applied during bloom and after symptoms are visible are not effective. Chemicals in the FRAC groups 7 and 11 are recommended at petal fall, and at two and five weeks after.

The inoculum remains in the orchard on the fallen leaves. Eliminating the infected leaves can help mitigate the disease. Trouillas also recommended cleaning harvest and spray equipment between orchards.

Carpophilus Beetle

The new insect pest Carpophilus beetle also appears to be invading tree nut orchards. C. truncatus is the only species of this sap beetle that causes direct damage to healthy nuts. Jhalendra Rijal, UCCE IPM advisor, said both adults and larvae can do high levels of damage. They attack nuts directly when on the tree, particularly after hull split. Carpophilus beetle damage was first seen in almond and pistachio and has been confirmed in walnut.

Rijal stressed that ground mummy sanitation is critical for managing this invasive pest. All mummy nuts need to be removed from berms, blown to the middles and shredded mechanically. Rijal said chemical control seems to be limited due to challenges with spray coverage and timing. Efficacy of commonly used insecticides in almond at hull split is not clear, he added.

Gill’s Mealybug

Gill’s mealybug is not a new pest, but there are new concerns that traditional insecticide products are no longer achieving season-long control with one application in May. Causes suggested by UCCE IPM advisor Idong Mokwunye include developing resistance and environmental changes causing this pest to be less synchronized than in the past.

Key considerations with Gill’s mealybug in pistachio production are exponential growth rates in the summer that result in high numbers of mealybugs per cluster at harvest. Monitoring for this pest from late summer through harvest can be done by looking for wet, shiny or black areas in the tree canopy. When honeydew or sooty mold is visible, clusters should be examined for mealybugs. In the fall and early winter, look for white aggregations of mealybugs on the undersides of the main scaffolds or on the trunk. Mokwunye said growers or managers should monitor populations to determine treatment timing at peak crawler emergence. Insecticides are generally most effective on the crawlers. Natural enemies can help with control.

Research focus is on application timing and single or combo treatment for control.

Nematode Management

UC Riverside Nematologist Andreas Westphal provided information on nematode management in almond as available tools are changing.

Nematode-resistant or -tolerant almond rootstocks are being developed and selected in trials to manage nematodes. New restrictions on chemical controls will require management decisions. Westphal said new application guidelines for Telone II are likely to impact efficacy. Field studies with pre-plant options show water delivery of Dominus results in high efficacy against root lesion nematode. Salibro, while not registered for use, has some nematode-suppressing capacity. Anerobic soil disinfestation can be an effective choice, and application simplification may be possible, Westphal said. High cost for materials is a downside.

Young Orchard Irrigation

Raymond Mireles, UCCE fruit and nut advisor in Fresno and Tulare counties, presented six steps to achieve optimum irrigation efficacy in young almond orchards.

“It is important to know where the roots are in young orchards,” he said.

1. Know the water application rate of the irrigation system.

2. Figure out how much water the orchard soil can store.

3. Note how much water the orchard is using.

4. Calculate the maximum allowable time between irrigations.

5. Estimate how long the system will take to refill tree water use.

6. Confirm irrigation schedule is on track with soil moisture or crop water stress measurements.

Other considerations to ensuring new trees get off to a good start is to recognize the difference between potted versus bare root trees, which can affect capillary action and gravitational pull. Locations of sprinklers or drip emitters and short irrigation sets with monitoring is advised.

With the limited root zone of young trees, Mireles also suggested digging into the soil to determine water access.