With almond harvest moving quickly in the Central and San Joaquin Valleys and pistachio harvest nearing completion and walnut harvest underway, nut growers are looking to turn their attention to post-harvest management tasks, an indication that the end of harvest is not a good time to let your guard down.

“Navel orangeworm (NOW) infestation was a big problem this year for a number of growers. This isn't a problem you can spray your way out of. NOW sanitation during the postharvest period must be the cornerstone of your program. Sanitation not only reduces the overwintering population, but the early generation levels for next year as well. Get mummy nuts off the trees and berms, swept and flail mowed,” reports Luke Milliron, University of California Cooperative Extension (UCCE) Orchard Systems Advisor in Butte, Tehama & Glenn Counties.

“Don't rely on winter precipitation to breakdown mummies. Although, mummy removal efforts can be aided by some previous rainfall, putting off sanitation too long could mean you miss the opportunity to bring in a shaker due to soft orchard floors. Just as with harvest samples, it can be informative to crack out some of these mummy nuts and get an idea of your infestation levels.”

In addition, Milliron suggests taking harvest samples is important to help in determining crop damage.

“It is critical to take the time to grab a harvest sample and crack it out during the post-harvest period. These samples give you a much sharper picture of sources of crop damage, than will be offered by processor grade sheets. Taking a sample from each block, each year, allows you to track damage levels and evolve your management practices,” warns Milliron.

Almond harvest damage evaluation resources can be found here.

Find walnut harvest damage evaluation resources here.

Navel orangeworm

Considering the serious threat posed by Navel orangeworm infestations, orchard sanitation ranks at the top of the must-do list immediately following harvest. Katherine Jarvis-Shean, UCCE Orchard Advisor, Sacramento, Solano and Yolo Counties, and Emily J. Symmes, UCCE Area IPM Advisor, Sacramento Valley, address the topic in the fall issue of the Sacramento Valley Walnut News issue (Fall 2019).

“Once harvest is complete, ensure that hullers, dryers, and areas surrounding orchards are cleared of nuts that may be harboring moth larvae. Sanitize orchards as part of your NOW management program by shaking/hand poling, blowing berms, and then flail mowing mummies prior to next season,” they report.

“Remember that walnut mummies on the orchard floor (middles and tree rows) provide overwintering survival sites for NOW, so even if you have few mummies remaining in the trees, blowing and destroying mummies on the ground helps reduce carry-over NOW populations.”

NOW concerns are not limited to walnut orchards. In a press release from the Almond Board of California, NOW sanitation in the almond orchard is just as critical, a position supported by American Pistachio Growers.

“With winter approaching, it is important to take the time to address mummy nuts that remain on trees or on the ground. Mummy nut removal and destruction are key to combatting navel orangeworm,” the Almond Board writes in their latest Almond Update.

Former UCCE Farm Advisor David Doll (The Almond Doctor) added to the need for total sanitation to avoid the risks presented by NOW.

“Winter sanitation is critical in managing navel orangeworm (as well as some other diseases) within almonds. Removing this past year’s remaining almonds – also known as mummies – is a time intensive process. Sanitation occurs by winter poling crews or by re-shaking the trees,” he reported.

Symmes said earlier this month that while first flight numbers for navel orangeworm have been moderate so far, she was quick to note there were exceptions. She indicated that a mild winter could lead to greater numbers of NOW as the winter moves into spring. She also notes that second and third flights of the moth are generally larger.

Time to cover crop, or not?

When it comes to planting cover crops, there are many advantages, and more than a few objections. To be honest, it comes down to weighing the benefits of winter cover versus the investment of time and money, and then choosing to opt in or pass on the idea.

While more than a few tree nut producers are planting cover crops, many others are more reluctant because of the added costs involved. But before an informed decision can be made, it is important to weigh the possible advantages.

Cover crops are generally accepted because of the benefits they provide to soil health and fertility. But there are other advantages. Water infiltration allowing less water use by volume, the benefit of nutrient and micronutrient in soils, aid in controlling weed problems and slowing erosion, and the added benefit of getting a jump on attracting native pollinators are all good reasons to consider their use.

In addition, there are some lingering assistance programs through the California Department of Agriculture that provides limited startup funds to get started using smart agricultural practices.

On the downside, the question remains whether the added cost in both materials and labor is offset by the possibility of higher quality, higher yielding orchards when cover crops are used.

If you haven’t considered the possibilities by the late fall season, it may be too late to get started this year. But it is never too late to consider the benefits versus the risks. Ask your orchard consultant, talk to growers who have adopted cover crop practices, and do some research on the Internet. One thing for certain, if the environment and weather continue to make farming more difficult in California, cover crops may become an absolute necessary practice for some farmers to survive.

Other post-harvest management considerations

Symmes and Jarvis-Sheen say post-harvest management should also include “pruning with BOT infection in mind.” They warn to be aware that dry conditions are required for pruning and hedging practices and the earlier in the fall this can be accomplished, the better.

Also, post-harvest weed management should be high on the list before winter weeds have a chance to germinate. It all starts with good scouting to identify the level of lingering warm weather weeds and to evaluate your annual weed management plan.

Also, October is a good month to remove older trees from the orchard by cutting and painting stumps to kill the roots before replanting can begin. More information for removing and replanting walnut orchards can be found here.

For more news on tree nuts as reported by growers and farm advisors, subscribe to the Tree Nut Farm Press e-newsletter.