As we approach another almond harvest season, there are some topics that need to be considered regarding potential insect damage. The 2008 harvest was one of the cleanest on record for most growers with regard to insect damage. Many huller/shellers reported a majority of their growers bringing in crops that fell below 1% insect rejects. Many organic blocks also recorded some of their lowest reject levels that year.
There were many blocks that did not shake cleanly at harvest, and record mummy loads can still be seen in many trees. Economics also prevented some growers from their normal winter mummy nut sanitation programs. Examination of these over-wintering mummy nuts will reveal live navel orangeworm (NOW). Even though hardshelled mummies may not have meat damage, the NOW larvae can overwinter nicely by feeding on their hulls.
Since these black nuts represent both an overwintering site and a potential egg-laying site for the first generation of NOW, some orchards will have high populations to deal with at harvest. Whether or not a grower chooses to go after NOW with in-season sprays (which are marginally effective on NOW), there are cultural considerations that need to be implemented for those who go into harvest with high mummy nut loads.
A Prompt Harvest
If hullsplit sprays are to be used, they need to target the beginning of hullsplit of the first sound nuts in the trees. More importantly, a prompt harvest is critical. By prompt harvest, I mean scheduling final irrigations to ensure proper dry down for early shaking when all nuts are split and beginning to dry (not waiting until all of the nuts on the tree are completely dry). Consideration must be made for trunk safety since shaking before bark moisture is sufficiently dry will result in bark slippage and potential Ceratocystis cankers.
Once on the ground, the nuts should be swept and windrowed as soon as they are sufficiently dry for the huller. Even leaving nuts a few extra days on the ground can result in significant damage. If nuts are to be stockpiled from a block with a known heavy mummy nut load, they should be immediately covered and fumigated to prevent further damage.
What about ants? In my observations, ants are still able to be controlled; however, the methods do not seem to be as effective or long-lasting as in the past. In years past, a single treatment with ant bait provided good ant control for the season. In some cases, blocks that were treated a previous year could actually skip the following year since the carryover effects lasted beyond the year of treatment. Currently this does not appear to be the case. Blocks, particularly those infested with Southern fire ant, usually need to be treated on an annual basis. This appears to be true even in blocks that are treated twice a season with a rotation of active ingredients for resistance management.
The prompt harvest and immediate hulling or stockpiling and fumigation is important for minimizing ant damage as well as NOW damage. How relevant this is to a particular orchard is dependent on the current mummy load in the trees at harvest, and the population of ants present.