By Robert Morris Prepared for ACDI/VOCA on March 10, 2009 Rotating fields to different crops each year is one of the most important and easily implemented disease control strategies for farmers. This practice avoids the buildup of many plant diseases in the soil. The longer the rotation before coming back to the crop, the less likely a disease will occur.  Because diseases usually attack members of the same plant family, it is best to avoid planting crops after each other that belong to the same family. Insect damage may increase when the same crop is planted in the same area over several years as well. Here are some common vegetables and the families they belong to. Tomato Family: Tomato, potato, eggplant, peppers Cucumber Family: Cucumber, melons, squash, pumpkin, gourd Lettuce Family: Lettuce, endive, salsify, Jerusalem artichoke Onion Family: Onion, garlic, leek, shallot, chive Carrot Family: Carrot, parsnip, parsley, celery Cabbage Family: Cabbage, broccoli, cauliflower, Brussels sprouts, kohlrabi, turnip, radish, Chinese cabbage, kale, collards, rhutabaga Beet Family: Beet, Swiss chard, spinach Pea Family: Peas, snap bean, lima bean, soybean Okra Family: Okra Corn Family: Sweet corn, field corn, wheat, barley, oats Some choices of crop rotations include Pea Family to Corn Family, Lettuce Family to Cucumber Family, Cucumber Family to Cabbage Family, and Cucumber Family to Corn Family. Rotating beans with a grain crop such as barley, oats, rye, wheat, or field corn or with a forage crop is very beneficial for root-rot control. One or two years in a grain crop is often long enough to prevent severe root rot when the field is not heavily infested with this disease. Some diseases that come from the soil are not easily controlled by rotation. Such diseases can live a long time in the soil and are not affected by rotation. Examples include clubroot that attacks the Cucumber Family, Phytophthora blight, and Fusarium wilt of several crops. Other diseases attack so many vegetables that they can survive indefinitely on many different plants including weeds. These diseases include Sclerotinia, Rhizoctonia, Verticillium and root-knot nematodes.  Many diseases can survive successfully because they can live on plants and plant parts left in the field after harvest. However they are unable to survive once the plants left in the field decompose. Destruction of plants and parts of plants left in the field after harvest can eliminate this problem. Plowing the field after harvest and before letting the soil rest can reduce the amount of disease that will survive.

            A YouTube video of a home gardener caught my attention recently who said that crop rotation (putting vegetables in different spots each time you plant to reduce disease and insect problems) wasn’t important for home gardeners. He said it was meant for commercial growers. https://www.youtube.com/watch?v=ki2Xc8s44sI             I could not disagree more! Crop rotation has been around for over 150 years as a good management technique for reducing disease and fertilizer problems, whether you grow a small number of plants or large numbers. I have seen this technique violated by small-scale growers in other countries with total disease devastation to tomatoes, peppers and cucumbers. Some vegetable families to keep in mind include: Tomato Family: Tomato, potato, eggplant, peppers Cucumber Family: Cucumber, melons, squash, pumpkin, gourd Lettuce Family: Lettuce, endive, salsify, Jerusalem artichoke Onion Family: Onion, garlic, leek, shallot, chive Carrot Family: Carrot, parsnip, parsley, celery Cabbage Family: Cabbage, broccoli, cauliflower, Brussels sprouts, kohlrabi, turnip, radish, Chinese cabbage, kale, collards, rhutabaga Beet Family: Beet, Swiss chard, spinach Pea Family: Peas, snap bean, lima bean, soybean Corn Family: Sweet corn, field corn, wheat, barley, oats             This technique switches the growth of vegetables to new locations every 3 to 5 years. It’s best to understand the families that vegetables belong to but if you don’t, then always grow vegetables that produce root crops (carrots, beets) in spots that previously had vegetables from flowers (tomato, pepper, eggplant) and follow that by growing leafy vegetables (lettuce, spinach, chard).             If you are using a single raised bed, then simply grow these vegetables in new locations in the raised bed so they aren’t grown in the same location. Don’t grow vegetables in the same location for 3 to 5 years.             An alternative method is to loosen the soil, lightly water it and then cover it tightly with clear plastic for three or four hot days in full sun, letting it bake. This method, called soil solarization, controls several plant diseases inhabiting the soil, as well as many insect pests and weed seeds.               In the Mojave Desert we see dry soil surface temperatures reach 170F routinely in the middle of summer. We need that temperature to about 8 inches deep so cultivate and water the soil before covering it in plastic.              This YouTube gardener may have success now without using crop rotation but he will learn this lesson the hard way in future years. Let’s not “throw the baby out with the bathwater.” Probably the worst part is that this propaganda will circulate on YouTube for many years to come and will lead home gardeners down a very dangerous and uneducated horticultural path.

 I put this on my blog in response to a question I recently received https://xtremehorticulture.blogspot.com/2015/07/gibberellic-acid-on-grapes-can-make.html Uses of Gibberellic Acid Robert L. Morris March 10, 2009 Gibberellic acid (also called Gibberellin A3, GA, and (GA3) is a hormone found in plants. Gibberellic acid is a very potent hormone whose natural occurrence in plants controls their development. Gibberellic acid promotes growth and elongation of cells. It affects decomposition of plants and helps plants grow if used in small amounts, but eventually plants develop tolerance for it. Gibberellic acid stimulates the cells of germinating seeds. Since GA regulates growth, applications of very low concentrations can have a profound effect while too much will have the opposite effect. It is usually used in concentrations between 0.01-10mg/L. Gibberellins have a number of effects on plant development including rapid stem and root growth and increase seed germination rate. Gibberellins are used in agriculture for various purposes. GA-3 is sprayed on seedless grapes to increase grape size and yield, and it is used on navel oranges, lemons, blueberries, sweet and tart cherries, artichokes and other crops to decrease or increase fruit set, delay rind aging, etc. These effects are highly dependent on concentration and stage of plant growth. GA is used to trigger flowering of sweet potatoes in breeding programs, to help tomatoes set fruit at high temperatures in the tropics, overcomes the need for chilling or long days to trigger flowering, and so is used in the tropics for breeding. Developing seeds are active sites of containing GA and studies have found increases in GA levels in seeds during germination. The germination of old seeds has been improved with use of GA. Applied GA-3 may trigger dormant seed germination, in many cases overcoming the need for special or prolonged dormancy-breaking conditions such as cold treatment, light, after-ripening, etc. Overcoming dormancy. Treatment with high concentrations of GA is effective in overcoming dormancy and causing rapid germination of seed. Premature flowering. If a plant is sufficiently developed, premature flowering may be induced by direct application of GA to young plants. Increased fruit set. When there is difficulty with fruit set because of incomplete pollination, GA may be effectively used to increase fruit set. The resulting fruit maybe partially or entirely seedless. GA has increased the total yield in greenhouse tomato crops both as a result of increased fruit set and more rapid growth of the fruit. Hybridizing. Pollination within self-incompatible clones and between closely related species may sometimes be forced by the application of GA and cytokinin to the blooms at the time of hand pollination. Increased growth. GA applied near the terminal bud of trees may increase the rate of growth by stimulating more or less constant growth during the season. Frost protection. Spraying fruit trees at full-blossom or when the blossoms begin to wither can offset the detrimental effects of frost. Root formation. GA inhibits the formation of roots in cuttings. Recipes Concentration parts/million GA mg Water ml (cup) Purpose 50 125 2400 (10 1/2) Early flowering 200 125 600 (2 1/2) Early flowering 800 125 160 (2/3) Blossom set 2000 125 60 (1/4) Seed germination 1% paste 125 5 ml (1 tsp.) lanolin Growth promoter Table 1. Preparation of bloom or sizing sprays of gibberellic acid for use on various table grape varieties Gibberellic acid is sometimes used in laboratory and greenhouse settings to stimulate germination in seeds that would otherwise remain dormant. It is also widely used in the grape-growing industry as a hormone to induce the production of larger bundles and bigger grapes, especially Thompson seedless grapes. In the Okanagan and Creston Valleys of Canada it is used in the cherry industry as a growth regulator. Effects of Gibberellic Acid Although GA is not listed as a “poison”, the following precautions should be observed: Flush with water any GA that may get into the eye. Avoid skin contact if possible. If skin contact is suspected, wash with soap and water. Do not re-enter an area after spraying until the GA spray is fully dry. Avoid ingestion of GA. The powder may be dissolved as specified below to give the desired concentration. Thinning and Increasing the Size of Table Grapes In varieties like Thompson Seedless, Flame Seedless, Perlette and a few other varieties (seedless grapes primarily) GA3 (gibberellic acid) is used for either thinning out the number of flowers which set fruit, a bloom thinning spray, or for increasing the size of the berries (referred to as a sizing spray which is applied about one week following bloom).  In some varieties both a bloom spray and one or two sizing sprays are generally applied. Not all varieties respond to bloom sprays for thinning. These varieties may use a gibberellin spray only for increasing the size of the berry. Grapes which produce seeds are generally larger than seedless grapes because seeds produce natural gibberellins which increase the size of the berries. One must be extremely careful when using GA3 on grapes. Each variety has a different tolerance level and one should not ‘experiment” or use more of the material than is recommended for any given variety. The gibberellin produced for commercial use in grapes is manufactured by Abbott Laboratories, Merck, and Agtrol. It is produced in both a powder formulation and a liquid formulation. For most home owners, the 4% liquid formulation (containing 1.0 gram/fluid ounce of formulated product) is the easiest to use. Before applying gibberellin to your vines, refer to the gibberellin product label and the variety write-up for levels which each variety will tolerate. Do not exceed the recommended dosages. Higher than recommended levels can severely injure the plant. Do not apply gibberellic acid to grape varieties not listed on the product label. The spraying guide put out by the companies for the use of 4% liquid on grapes refers to actual grams of gibberellic acid applied in the finished spray per acre. Conversion for only a few grapevines is often difficult; so, refer to Table I below in which the

Differences in trees can be because of their genetics and how they were propagated in the nursery, differences in soil in very small areas and management. Q. We had 3 African sumac trees planted in our backyard 1½ years ago. We treated them the same during this time but the tree the farthest away has large dark green, healthy leaves and the other 2 trees have lighter color leaves and they are curled.  A. African sumac is propagated from seed so there is a lot of variation among trees. They also come in male and female trees so let’s remember that as well. Seeing seed pods in African sumac is a good indicator the tree is female.             Lighter leaf color can mean the trees are not getting enough nitrogen fertilizer, they are watered too frequently, or the soil does not drain water quickly enough. Because these trees were not planted by you, it’s not known if the soil where these trees are growing drains water similarly or not.             Let’s tackle the fertilizer issue first. Apply a high nitrogen fertilizer in the basin of the trees just before an irrigation. Let the irrigation water transport this high nitrogen fertilizer to tree roots. If nitrogen fertilizer is the culprit, you should see a change in the leaf color before one week. Moisture sensors like this inexpensive type used for houseplants can tell you the approximate time to water. Push the probe into loose soil in several places to get a rough idea when the soil is wet or dry.             Inexpensive soil moisture meters, such as they use for house plants, can give you a rough approximation if the soil is wet or dry and when to irrigate again. Water these trees only when the soil is beginning to dry, never while the soil is still wet. If trees are watered too soon and the soil is still wet, leaves can discolor and become yellow rather than dark green. But the differences in leaf density between the trees indicate a difference in the amount of water they are receiving.

Leaf drop on any tree can happen if the flow of water from roots to the top is interrupted. Q. We have a five-year-old apricot tree. Previously, it’s always seemed happy but this year it leafed out beautifully, then it started dropping its leaves. Apricots are still on the tree but not developed yet. Then this week ½ of the branches on one side are leafless. Another angle of the same tree. A. Pictures were sent to me of this tree so let me explain what I saw. The apricot tree is 6 to 8 feet tall with a similar spread but leaning strongly toward the light but away from some taller shrubs on one side. Leaves are on the ground and have dropped from the side away from the light. The week it dropped its leaves was a hot week and then it got cool again. Apricot sap dripping from limbs or the trunk can be a sign of borers particularly if you see it when it gets hot.             Trees drop their leaves because they are not getting enough water. They also drop leaves if it’s too dark, but I think in this case it’s a water issue. A lack of water can be from not enough water applied to the soil under the tree, borer damage in the trunk or several large limbs or a disease problem. Sap dripping from the trunk can indicate wet soils. Add lots of water and then hold off watering until the soil has begun drying.             I’m going to rule out the disease possibility because it is highly unlikely in the desert. Borer damage is a possibility except the leaves are dropping at the wrong time of the year and from half the tree instead of a branch. Borers cause leaf drop during the heat of the summer, June or July, frequently affecting an isolated branch or two. So, let’s rule out borer damage. Wood chip mulch applied several inches think is good for fruit trees planted in desert soils but keep the wood chips a foot from the trunk for the first few years to prevent collar rot. Collar rot on fruit trees looks alot like drought.             It is possible this tree had gotten larger and was not getting enough water. Along with a shortage of water, the distribution was not over a large enough area under the canopy to satisfy its roots. As trees get larger, they require more water distributed to a larger area under the canopy.             To test this idea, use an inexpensive sprinkler on the end of a hose, connected to a mechanical timer at the hose bib or faucet. Put the sprinkler about 2 feet from the trunk of the tree and turn on the mechanical timer for two hours so it wets the soil deeply in an area about 5 feet in diameter. Do the same thing to the other side of the tree. Do this twice a week for the next two weeks and let’s see if the tree responds.             If I’m right, you will see new growth coming from the limbs that are bare and where there are leaves, you will see new growth. If this is the case, increase the number and size of the emitters. Place one drip emitter scattered about every 2 feet under the canopy of the tree. The water should penetrate the soil about 18 inches deep after an irrigation.

Q. I have two dwarf magnolia trees in my courtyard in front of the house. They started dropping leaves and they’re kind of scarecrow looking. What do I do? The Mojave Desert is not the easiest place to grow magnolias. Magnolias, Southern Magnolias in particular, will have difficulty growing in a desert climate. A. Let’s get something out of the way early. This is not magnolia country so they will require extra care and attention here. I hate to sound like a broken record, but it is either water or soil improvement or both.             Is it planted in rock? That’s a mistake if they are. These are not desert plants so they will not like rock. The soil around them should be covered with a 4-inch layer of woodchips instead. Find the perfect spot, like planted in a lawn, and they may flourish for a few years. But don’t plant them in a desert landscape.             How many emitters do they have? They will need at least four if they are four or five feet tall. These will be placed in a square pattern about 18 inches from the trunk. This will be enough until they get about 10 feet tall and then you will probably have to bump it up to about six or eight emitters spaced evenly under the tree canopy.             Making sure these trees get more water will stimulate more leaf development and a denser canopy. The water should be on long enough for it to drain to about 18-24 inches deep after each watering. Use a steel rod like a 3-foot long rebar to judge the depth of irrigation.

Q. Do you know what these bugs are? They don’t seem friendly to me. Leaffooted plant bug seen now on pomegranate, one of their favorites. A. They are out there now and multiplying fast. Immature of the leaf footed plant bug. A very nasty bug and will feed and multiply on lots of stuff in your fruit trees, nut trees, vegetables and herbs. If you look in there you will see the Mom protecting them from predators. Leaf footed plant bug adults and advanced juveniles on citrus. Vacuum with a cordless vacuum cleaner when young like this. If you don’t mind pesticides then try pyrethrins and synthetic pyrethrins. If that doesnt work then carbaryl (Sevin) insecticide but it is hard on honeybees so spray at dusk when the bees have returned to their hive because they cant navigate without sunlight. Leaffooted plant bug later in the year on pomegranate. Watch out for them on pistachio, almond, tomatoes, and other vegetables, fruit and herbs.

Q. I have a cactus garden that faces west. Every summer I hang sheets on a clothesline to shade them so these cacti dont burn from the direct westerly sun and heat. The sheets get stuck in the cactus when the wind blows and pulls the small ones out of the ground. If I don’t protect the cactus this year, will they die? Some cacti like barrel cactus can handle the Mojave Desert environment with no problems as long as you don’t water them too often. Photo taken at Las Vegas Springs Preserve. A. It depends on the cactus and where it comes from. Many people don’t realize that not all cacti require the same type of environment. They are as individualistic as we are. Watering a Joshua tree too often will kill it. It is a Yucca.             Cacti are found in a variety of climates, from our harsh desert Southwest conditions, to shade-loving cacti to drought tolerant cacti that survive on moisture from ocean fogs. For this reason, some cacti may thrive in your Western exposure while others need protection. This is Yucca pendula or soft Yucca and is native to the southeastern United States. It cannot handle intense sunlight so it should be planted in an area protected from strong sunlight in the afternoon.              You should know by now which cacti are struggling and which are not. Yellowing or turning white on the west sides of these cacti is sunburn. Move these cacti to new locations with filtered light or an eastern exposure. They will recover. Leave the ones which seem to handle the intense sunlight, alone. Watering a cactus too often or fertilizing it too frequently can cause it to grow faster than it can support itself.             Learn their common and scientific names and where they come from. Sometimes the presence of a covering of dense spines or “fur” can provide a clue about their sensitivity to direct sunlight and their need for protection.

Q. I am growing new cacti from pads cut from the mother plant. You recommended I amend my soil with either compost or manure before planting the pads. I used a local planting soil which was cheap but not a good decision, I discovered. Can I amend this soil and “fix” it?   When planting cactus pads, make sure pads are planted north – south so that one side of the pad receives morning sun and the other side of the pad receives afternoon sun. Add manure or compost to the soil. Don’t water too often. Use a soil moisture sensor like the one pictured to gauge when to water again. A. You probably can. However, the soil should not be “fluffy” but firm after it’s been watered. If it’s “fluffy”, the cactus will fall over when it gets taller. It will also fall over, or possibly die, if watered too often, watered frequently with small amounts of water, or if water is applied only around its base. Use native desert soil whenever possible, mix in a small amount of manure and build a three-foot basin around the plant for containing enough water applied to it. Water it every three or four weeks in the summer, filling the basin to its brim. The area around the pads can have a basin built to keep the water from getting away. Monitor the soil moisture to know when to irrigate again.             Make sure all cuts have healed before planting the pad or it can become infected and rotten. To be done on the safe side, apply a copper fungicide like Bordeaux to the bottom fourth of the pad before planting. This helps keep wounds from rotting when it first get started. If laid flat the pads will curl over night. Stack them vertically until they are used.             Plant the entire pad so its flat surfaces are facing east and west and one third of it extends below the soil. Water the entire basin and let it soak into the soil 12 inches deep. The roots will form from the pad using stored water taken from them.

Q. I see landscapers putting new plants in the ground without removing the black plastic pots.  I see these same plants thriving and doing a whole lot better than some of my own which I have planted in amended soil and surrounded with mulch. And that really ticks me off. A. Sometimes it doesn’t seem fair. You do everything right and your hard work doesn’t seem to pay off. At least in the short run. Plants will grow in water if it has air bubbling through it and fertilizer available. That doesn’t mean it’s a healthy environment for their long-term survival.             Soils used to produce plants in containers are inexpensive to make, lightweight so they are easy to carry and transport and drain water quickly. Plants growing in containers must be watered often and “fed” with regular applications of fertilizer. Container root environments encourage fast plant growth but are not intended for the long haul.             Recently, I saw one-year old Western Redbuds in containers for sale at a local box store. The soil was sawmill waste plus fertilizer mixed in it and they were four feet tall! However, the trees were poorly rooted in the container, they had trouble staying upright, but they were big for one-year old trees!             Plants in containers will continue to do well after planting in the ground, container and all. This is because the containers, together with the plant roots, are surrounded by cool soil and no longer punished by intense sunlight and high temperatures. After planting, plant roots grow through the bottom of the container and into the surrounding soil in just a couple months. The top of the plant grows quickly but its roots are surrounded by the plastic container, impeding its establishment.             Vigorous plants survive through this ordeal, but more delicate ones will struggle and probably not. Landscapers are long gone by the time plants begin struggling. Some become weak and struggle after a couple of years growing with this plastic container surrounding its roots.             Plants always perform better over the long term if planted into the soil and cared for properly. Some may struggle for the first few years. But most plants perform best if our soil is amended at the time of planting, giving them a good start. Stake larger plants the first year and water so that at least half the roots under the canopy are getting water as they continue to grow.             Apply enough water so it infiltrates into the soil 1 foot deep for small plants and 2 feet deep for small and medium sized trees. Wood chips on the surface of the soil improve it so that the majority of its “feeder roots” are growing in the top few inches which they love but takes a season or two before they “catch”.