There's a new edition of our Newsletter,
edited by Monique Rivera,
UC Subtropical Crops Entomologist -
- A “boring” problem that's generating a big interest in southern California
- How ants can be “good” in ag production systems
- Is Eucalyptus a Safe Material for Mulching Trees?
- Botryosphaeria Gummosis and Dieback of Citrus
- The online Lucid Key, Thrips of California, has been updated
Here's the Fall newsletter of Topics in Subtropics, and it is on time. Winter hasn't started yet, but get ready.
And the topics are:
- Real-Time Sensor for Early Detection of Citrus Huanglongbing (HLB)
- The 2016 International Citrus Conference
- UC Riverside Scientists Evaluate Trunk Injections of Pesticides for The Management of Ambrosia Beetles in California Avocados
- An Overview of Mango
- Water Based Latex Paint as a Means to Track Ambrosia Beetle Activity on Infested Trees
It ain't over yet, and this last week we had a wonderful 2 day meeting with folks who have dealt with drought in many different ways. Here are presentations made by people from Israel, Australia and California. Soon the actual videos will be available, but now see the powerpoints.
The grower panels are wonderful, but are not uploaded at this point
DAY I: UNDERSTANDING IRRIGATION WATER MANAGEMENT
Session I: California Response to Drought
9:15am // Overview of California Drought Response
Session II: Technology of Water Management
9:45am // Soil Water Sensing
11:00am // Salinity Measurement
12:00pm // Precision Water and Fertility Management During Deficit Irrigation
Session III: Alternative Water Supplies
2:00pm // Effects of Irrigation With Poor Quality Water on the Soil - California Experience
3:00pm // The Challenge of Sustainable Irrigation with Water High in Salts: Lessons from Dates, Olives and Grapevines
Session IV: Water Management Strategies During Drought
Day II: WATER MANAGEMENT FOR INDIVIDUAL CROPS & GROWER EXPERIENCES
Session V: Technology Demonstrations
8:30am // Using the Pressure Chamber for Drought Mangagement Decisions
9:00am // Irrigation System Evaluation
9:30am // Salinity Mapping for Water Management
Session VI: Conncurrent Breakout Groups
10:30am // Citrus - Israeli Experience: Long Term Effects of Deficit Irrigation, Salinity, and Rootstocks on Orchard Productivity
10:30// Almond Irrigation, the Israeli Experience
11:15am // Grapes - Wine Grapes Irrigation - Coastal Vineyards
11:15am // Deciduous Nut Crops - Almond Irrigation - Israeli Experience
1:00pm // Avocado - Israeli Experience
1:00pm // Grapes - Wine Grapes Irrigation: San Joaqin Valley
1:45 // Subtropical Crops - California Experience
2:00pm // Deciduous Nut Crops - Walnut Irrigation
2:30pm // Grower Panels
3:15pm // Concluding Remarks
Soil likes to be covered at all times. It doesn't “want” to be exposed to the elements, so you either cover it (plants, asphalt, paper etc.) or it will cover it for you with plants (weeds). If it can't be covered fast enough, it disappears – erodes. This can be from wind or rain or just natural movement down slope. Plants that are managed for other than their agricultural return are called cover crops, although they can also have a crop that is saleable. Often weeds can be managed to be a cover crop, as well.
We are looking at a possibly wet winter and many tree crops grown on hillsides and sloping ground are prone to soil erosion. Covers can be grown year round, but that usually means they require water all year round. That means they need an irrigation system dedicated to their needs. It also means having extra water which may be limiting.
A winter cover crop that grows out in the winter, does its thing (although that “thing” can include lots of other things, e.g. insectary, nutrients, water retention, etc.), and then dies or goes dormant, can be ideal. It also requires less water than a permanent cover.
But there is a big problem here. Establishment of an introduced cover still requires water. Rainfall in Southern California is erratic and there may be early rains to germinate seed, but it may not be consistent enough to get the plants established. In fact, they may die for lack of further rain or be delayed.
Delayed germination means that soil is cooler and there is less growth. The real growth may occur after there has been sufficient rainfall by January and February when the soils are cooler and there is even less chance for growth
So when rainfall is doing its worst, there's no effective cover. Or what cover there is, is what has germinated from “native” seed. It may not have the characteristics you want for management: low stature, low entanglement with the trees, low water use, holds the soil without holding up harvest, etc.
So what do you do? There are several approaches. You can move the sprinklers out into the middles and irrigate up the seed. If you are in a limited water situation, you can do alternate middles, not cover cropping the whole area, or every third middle. Whatever it takes to break the surface flow of water. Or you can turn to mulching. Put down sufficient mulch in a middle or every other middle to break overland water flow.
Cover cropping is easier than mulching, but it takes water and timing.
Below are two websites with descriptions of cover crops and how to distinguish them from “weeds”. Often a good cover can be the residential weeds. A low–lying cover allows pickers in to get lemons without mess and fear of snakes. It also means that it can be more easily treated (mowed, weed whipped) at the end of the rainy season to reduce fire hazard.
1) Characteristics of different cover crops
2) Weed identification from the UC IPM
Some call it tip burn which is often what you see on an avocado as it goes into flowering. The areas where avocado are grown typically have a lot of salts in the water, but also specific salts like sodium and chloride. Over the irrigation season (which is all year long there is little or no rain), the salts in the water/soil are taken up by the tree. In adequate rainfall years, there is enough water to leach those accumulated salts from the root system. When we go for several years with low rainfall and we keep irrigating with the poor quality irrigation water, the trees develop die back at the tips and is conditions worsen more and more of the leaf is called. This can get to the point where you can not call it die back any longer. It's called leaf drop. I've recently seen a number of orchards that are completely defoliated. No leaves. We have had a number of homeowner calls asking what the problem is and what they can do about it. The damage is done and those leaves are not coming back. It's possible to reduce the damage if one acts early on by applying more water than is usually applied to aid the leaching process, but if it is poor quality water, there will still be damage, but possibly not defoliation. With high priced water or where water is being rationed, many growers and homeowners do not have themake the option of putting on the excess water. There is no chemical or equipment that is going to make the situation better. When you trees defoliating, you want to cut out those that are diseased or you know have been poor producers and put what water you have on the remaining trees in better condition.
This advice is good for other evergreen tree crops like citrus, although they are not as sensitive as avocado. Avocado is an indication of how bad it really is.