- Author: Ben Faber
With all the rain last year, even extending into August and now with the rains since December there is a lot of natural ground cover growing, When it gets out of hand, we call it weedy. It might still serve the purpose of protecting the ground from erosion, but it can become an impenetrable mess and if allowed to go into summer, a major fire hazard. In the case of some young orchard, the malva and mustard is bigger than the trees themselves. Getting control of them before they get woody and go to seed is easier earlier than later. So it's time to do something about them if you haven't done so already.
A common practice on flat ground is to mow the middles and then weed whack/whip the tree row up to and around the tree trunk. In the case of trees that have their canopies down to the ground or near the ground or that have created a thick leaf mulch, there's not usually much weedy growth near the trunk. Then weed whacking around the canopy is not much of a problem. If on a slope like most avocados, it's a big, expensive, laborious, hot, sweaty, arduous process of weed whacking. Just waiting long enough for the leaf mulch to create a barrier to weed growth and for the canopies to grow out to rob the sun from the surface undergrowth.
In young trees without a large canopy, it can be a really difficult process of getting those weeds near the trunk. Care must be taken to avoid damage to the trunk. In a couple of recent examples, weed whacking got right up and on the trunks and significant damage was done to the trees. When a wound occurs in any tree, a process kicks in to generate tissue to cover the wound, much like what happens with humans and wound cuts. There's a scar left, but it heals over. If the wound is too large, many trees cant cover the woody tissue fast enough. The wood beneath the cambium ( the green tissue below the bark) is prone to fungal infection and eventually the fungus eats away at the interior of the tree. If the wound is large enough and girdles the tree, all the nutrients from the leaves feeding the roots is cut off. The photosynthate sugars that keep the roots functioning, and the roots stop doing what roots do. This is absolutely true is citrus and most other orchard tree crops. But not avocado.
When making a cross section of most trees, it's possible to see the growth rings – the growth increments that appear each year. The tree starts and stops growth each year and it's possible to clearly identified in what year there was more or less growth. In long lived trees like redwood, it's possible to identify years when certain events happened – the year of Lincoln's Gettysburg Address, for example. This growth habit is called ring porous.
In the case of avocado, it has a growth habit called diffuse porous. There is growth throughout the year and the rings are nor clearly delineated, if at all. It's because of this possible active growth occurring, that the avocado can often cover over damage that is quite extensive. After a fire, given time, mature avocado trees can summon up energy to recover to a great extent. It's not so true of young trees, however. Avocados still have a greater regenerative capacity than a lemon tree, and if the damage is to just one side of the tree, there's a very good chance of recovery.
But these young tree are severely impaired. They do have a chance of recovery, but the damage is extensive and the trunk is fully girdled. Only time will tell if they do recover. If the tree were only a year old, it would be a good idea to pull them and start over. But a number of these trees are three years old and have had a lot of investment in them besides their initial nursery cost – pruning, weeding, irrigation, fertilization, etc. It is heart breaking to see damage like this after so much attention has been paid to them.
And the best thing is to let the tree recover on its own. Use of pruning paint actually impairs tissue regeneration. The grower asked if a kaolin protectant like Surround might be used to provide some sun protection. Since that breathes, it might be a good idea. It might also be a good idea to apply some trunk wraps. These were taken off in order to prevent earwig and snail harbor which can cause significant damage to young trees. But they also provide protection from overly aggressive weed whackers. It is always a compromise when making these decisions.
- Author: Ben Faber
The destruction after a fire can be pretty gruesome and sad. Many times, though the fire moves through the orchard so fast that, even though the canopy has turned brown, there is a good chance the trees can come back. It all depends on how much damage has been done to the trunk. If the fire has substantially damaged the base of the trunk, it is unlikely to come back, even if the canopy is still green. That is the saddest thing, because you think you've dodged the bullet, but if the trunk is too damage, the canopy collapses gradually over a few weeks. However, the canopy may look a goner, but if the trunk is still intact, the tree will come back and may still be as productive as before.
The thing to look for at the base of the trunk is the discoloration. If it's black, it's probably not coming back. However, it can come back if after a few weeks you don't see the pencil-sized cankers that indicate that the sap has bubbled to the surface (see photo 1 below). If after a few weeks, the trunk is still clear of those bubbles (photo 2), even though the canopy looks gone, it is quite likely to come back.
It's also possible that the trunk may be damage in just one part of the trunk and not on the rest. In this case, it can also come back. The problem with these ones, is that they may come back and given enough time will be good trees again. But if they haven't recovered enough and there's a sudden heat spell, they may go down suddenly as if they had been burned again. That's the way they will look, like they have been burned again. Given enough time, though the avocado will grow from good areas to cover the poor areas and the tree may be productive again.
Avocados are amazing in their ability to recover. Eucalyptus can do it. But you singe the trunk of a lemon, and good-bye lemon.
Fire Information:
http://ceventura.ucanr.edu/Agricultural_Threats/Fire_Information/
Photo 1 and 2.
- Author: Neil O'Connell
Since the first publication of this article on vole damage in citrus, a recent field observation regarding vole activity is worth noting. Voles prefer a situation where there is cover and shelter generally from weed or grass. In some orchards established in the last few years a plastic strip has been installed along the tree row for weed management (Fig 1). These strips appear to be offering a sheltered environment for vole activity in some cases (Fig 2). Recent observations in two such installations, one a block planted in 2013 and the other an eight year old planting exhibited significant vole activity. The young orchard at this point does not exhibit obvious tree damage although active tunneling is apparent (Fig 3). In the older orchard feeding damage to the trunks is very obvious (Fig 4).
Meadow Mice (Voles) can cause serious damage in a citrus orchard resulting in partial or complete girdling of a tree (Fig 5). Trees often exhibit damage to the bark of the tree from the soil line up 6-8 inches (Fig. 6 ). On close inspection, an open hole 1-1.5 inches in diameter may be found at the base of the tree (Fig 7).
Five species belonging to the genus Microtus are found in California, two of which “Microtus californicus” and “M.montanus” are reported to cause damage. Damage has been reported in permanent pasture, alfalfa, hay, artichokes, Brussels sprouts, carrots, cauliflower, potatoes, sugar beets, tomatoes, grains, nursery stock and the bark of apple, avocado, citrus, cherry and olive trees.
Microtus are often found where there is grass cover. They generally do not invade cultivated crops until the crop is tall enough to provide food and shelter. Meadow mice are active all year round. They forage at any time during the day or night but are chiefly nocturnal. They are usually found in colonies marked by numerous 2-- inch wide surface runways though matted grass. Small brownish fecal pellets and short pieces of grass stems along the runways are evidence of activity. The burrows consist of extensive underground tunnels, nest chambers and storage chambers. Home range is typically small, less than a 60 foot radius in the case of “M.californicus”. All meadow mice swim well. Therefore, irrigation ditches will not serve as effective barriers against meadow mice movement into fields. Meadow mice may forage beyond the sheltered runways. Food consists of tubers, roots, seeds, grain, and succulent stems and leaves.
Females breed at 4 to 6 weeks of age with litter size of “M.californicus” averaging around 4. Under natural conditions a female Microtus may produce from 5 to 10 litters a year. The major breeding season corresponds with the season of forage growth. Microtus populations build up to a peak every 3 to 4 years, followed by a rapid decline during the next breeding season. The exact causes of the cycle of buildup and decline are not known, though disease, food shortages, physiological stress from overcrowding, and other factors may be involved. It is assumed that in cultivated areas Microtus populations are permanently based in favorable habitat such as roadsides, canal banks or adjacent noncultivated land. Invasion of cultivated cropland occurs when the population builds up or when the wild habitat becomes unfavorable. Coyotes, badgers, weasels, snakes, hawks, owls, herons and gulls are among the principal predators. It is believed that predators are not able to prevent or control a population eruption because of the birth rate of the fast breeding Microtus population. Meadow mice are classified as nongame mammals by the California Fish and Game Code. Nongame mammals, which are found to be injuring growing crops may be taken at any time or in any manner by the owner/management. The most effective management options in an orchard situation are a reduction in ground cover and the use of toxic baits. Meadow mice are cover dependent. In situations where cover removal is not possible or is insufficient to solve the problem, the next best option is the use of toxic baits. Many bait carriers are used (e.g., oat groats, wheat bait). Baits: Crimped oat groats are the most satisfactory bait although crimped whole oats are used (e.g., oat groats, wheat grains, pelletized formulations, etc., but crimped oat groats have typically been most effective). The primary toxicants used for meadow mouse control include zinc phosphide, diphacinone, and chlorophacinone. Directions for management including baiting can be obtained by contacting the Agricultural Commissioner's Office. * Portions taken from J.P.Clark Vertebrate Pest Control