As harvest winds down to a close the hard part of my job as a Plant Doctor is slowing down as well. But just because the crops have been harvested doesn’t mean that there aren’t pests to deal with. Now is the time to evaluate how things went during the season. After harvest and during the winter when trees and vines are dormant is a good time to see what may be in store for next year as well.
Almond harvest, seen below, is generally finished in September. Walnuts go into late October.
In the nut crops, almonds and walnuts, I have samples of the nuts from each block take before the nuts were removed from the field. I crack the nuts open and look for any worm or other pest damage. I’ll crack about 200 nuts on every block (my friends who bake get the good ones). On almonds, ants can eat the nuts when the hulls have split and when the nuts have been shaken off the trees and drying on the ground. If your ant control wasn’t good, you’ll see damage in the crack outs. Other damage that can be seen on almonds is damage from stink bugs.
Stink bug on almond
Stink bug can damage nuts late. Kernels of damaged nuts either become wrinkled and misshapen, or if already hardened before bug damage, will contain a black spot at the puncture site.
Navel Orange worm in almond
Another pest you can find in either nut is the Navel Orange worm. Not really sure where it got it’s name but it is a pest primarily of nuts. Can be a pest in pomegranates too. They usually attack the nuts late, after the hull and husks have split. The key to controlling this pest it to make sure the populations do not get out of control early in the season. Since they go into the nuts, they are almost impossible to control once they get in.
Another worm that can be found in walnuts is the Codling moth. If you see damage from Navel Orange worm in walnuts it generally means your Codling moth control probably wasn’t very good. Navel Orange worm usually gets into walnuts through the holes left by early Codling moth damage.
After the leaves are off of the trees it is important to take a look and make sure there are no nuts still hanging in the trees. These “mummy” nuts will be places where Navel Orange worm will survive over the winter. Mummy nuts are removed from the almond trees with workers using poles to knock them down. If there is enough rain, most of the nuts will fall as they get heavy with moisture. You don’t want to have more than an average of 1-2 mummy nuts in a tree throughout the orchard. My job is to go around and count these mummies and determine if they need to come off.
Another important task in the winter, on all the tree crops, is to examine scaffolds, limbs, branches, and prunings for scale insects and mites. Walnut scale, San Jose scale, frosted scale nymphs, and European red mite eggs can all be found by examining the wood during the dormant period. I’ll gather about 100 samples of smaller twigs for every block. I usually bring them home and look at them in the warmth of my kitchen.
Pile of frass at entrance of peach twig borer hibernaculum.
In the late winter, usually after the first of the year, I’ll decide, based on what I’ve found during the checks I’ve mentioned above and on observations made during the year, what stone fruit and almond trees will need a “dormant spray”. This is a spray that we put on the trees just before they start to wake up for spring. Disease such as shot hole and leaf curl will over winter as spores on the wood and those can be controlled in the dormant spray. Scale, mites and any worms that over winter in the trees, can also be controlled at this time. Peach twig borer overwinters on the tree as a first- or second-instar larva within a tiny cell, called a hibernaculum, that is located in crotches of 1- to 3-year-old wood, in pruning wounds, or in deep cracks in bark. The overwintering site is marked by a chimney of frass and is especially noticeable when first constructed or before winter rains set in. Larvae emerge in early spring, usually just before and during bloom, and migrate up twigs and branches where they attack newly emerged leaves, blossoms, and shoots. Dormant spray will help control this pest.
Grapes generally don’t need much attention after harvest. This year however, the vine mealybugs were so bad I am considering doing some post harvest sprays. These pests will go down below ground and spend the winter on the roots, only to come back up again next season. The fewer going down will mean less coming back up, or at least I hope so. These warm winters are not helping. We are not getting the winter knock down of pest populations we usually see. Monitoring for these pests during the winter entails digging around at the base of the vine to see what kinds of population levels are hiding out.
Citrus leaves with citrus leafminer larvae,
Citrus is a year round crop. The new crop is developing as the old crop is maturing and getting ready to pick. Trees are always green and pests can be found all year. Most of the time pest are not much of an issue in the winter. But when the winter is warm, like it has been the last few years, some pests can keep active. Red scale usually is dormant in the winter but last winter you could pick up males flying around in the traps even in the winter. So going out a couple time a month to keep an eye on what is going on is a must. Bean thrip is sometimes active in these warm winters and some of the export markets don’t what to see them so if fruit is going to these markets, bean thrip need to be dealt with. If not, I just ignore them. Citrus leaf and peel miners can also remain active in the fall if temperatures remain warm. Citrus tree will put on their last flush of growth in the fall so you want to keep these miners off the leaves.
About this time of year we are expecting (and hoping) for rain so sprays on the citrus for brown rot and Septoria spot are being applied. Certain export markets don’t want certain disease so you need to keep the fruit clean. As the weather gets cooler and hopefully wetter, the snail will come out from under the trees and make baiting for them easier. They are a real pain. Did you know snail eat oranges?
Alfalfa will go dormant when it gets cold enough. The only thing to watch out for there are aphids. Certain ones, like cowpea and blue alfalfa aphid can damage the plants if they build up to significant levels.
Last but not least, WEEDS. In all the crops and on the bare row crop beds, weeds will be something to contend with all winter. If it gets cold enough weeds will stop growing or grow slow enough not to worry about too much. There are spray that will go out that will keep them from coming up but most need to be rain activated so if we don’t get enough rain, they do not work very well. We need all the moisture we get in the soil, not being sucked up by weeds. Weeds are my constant bane of existence all year long.
What else does a plant doctor do in the winter? Education!! Plenty of meetings to learn and keep up with all the new technology, pest trends, research, etc. In California I need 40 hours of continuing education to keep my state license but I generally get more than that. So much to keep up on. Always learning.
Note: Thanks for the UCIPM website for all the great photos. These are much better than I could take.