- Author: Ben Faber
Years of drought, and a stressed tree are a perfect set up for navel oranges and fruit splitting.
The days have turned cooler and suddenly out of nowhere there is rain. That wonderful stuff comes down and all seems right with the world, but then you notice the navel fruit are splitting. Rats! No, a dehydrated fruit that has taken on more water than its skin can take in and the fruit splits. This is called an abiotic disease. Not really a disease but a problem brought on by environmental conditions.
Fruit splitting is a long-standing problem in most areas where navel oranges are grown. In some years, the number of split fruit is high; in other years it is low. Splitting in navel oranges usually occurs on green fruit between September and November. In some years, splitting may also occur in Valencia oranges but it is less of a problem than in navel oranges.
Several factors contribute to fruit splitting. Studies indicate that changes in weather including temperature, relative humidity and wind may have more effect on fruit splitting than anything else. The amount of water in a citrus tree changes due to weather conditions and this causes the fruit to shrink and swell as water is lost or gained. If the water content changes too much or too rapidly the rind may split. In navel oranges the split usually occurs near the navel, which is a weak point in the rind.
Proper irrigation and other cultural practices can help reduce fruit splitting. Maintaining adequate but not excessive soil moisture is very important. A large area of soil around a tree should be watered since roots normally grow somewhat beyond the edge of the canopy. Wet the soil to a depth of at least 2 feet then allow it to become somewhat dry in the top few inches before irrigating again. Applying a layer of coarse organic mulch under a tree beginning at least a foot from the trunk can help conserve soil moisture and encourage feeder roots to grow closer to the surface.
If trees are fertilized, apply the correct amount of plant food and water thoroughly after it is applied. If the soil is dry, first irrigate, then apply fertilizer and irrigate again.
- Author: Ben Faber
To help Ventura County's citrus community better understand the nature of the ACP epidemic — and the bitter lessons from Florida's failure to address it proactively — Farm Bureau and the ACP-HLB Task Force will host a workshop on Dec. 2. As speakers, we've invited three experts whose presentations were among the most compelling at last February's International Research Conference on HLB in Florida:
- Mike Irey, director of research and business development for Southern Gardens Citrus (which farms nearly 15,000 acres of oranges in Florida), who will speak about conditions in his state and provide an industry perspective on what it's like to live with HLB for a decade;
- Dr. David Bartels, an entomologist at the U.S. Department of Agriculture's Mission Laboratory in Texas, who will discuss his analysis of HLB survey data and what it can tell us about possible HLB infection sites throughout Southern California;
- Dr. Neil McRoberts, an epidemiologist and associate professor of plant pathology atUC Davis, whose computer modeling and research into the economic and social factors affecting disease spread can help guide development of an HLB management strategy for California.
The workshop will be from 1 to 4 p.m. on Wednesday, Dec. 2, at the Museum of Ventura County, 100 E. Main St., Ventura. It's free, but RSVPs are required. Please contact us at info@farmbureauvc.com or (805) 289-0155 if you plan to attend.
- Author: Ben Faber
Another impact of the drought? There have been reports of a sunken, leathery patch around the blossom end (opposite of the stem end) of citrus fruit. This has been reported on lemons, limes and mandarins, but I am sure growers are seeing it on oranges, as well as other citrus relatives. This is an abiotic problem caused by a lack of calcium to the fruit, a problem with the plant's growing conditions, not a disease. This is a serious disorder found in various fruits and vegetables, such as tomatoes, melons, peppers and eggplants
Blossom-end rot begins as small tan, water soaked lesions on the blossom end of the fruit. The lesion enlarges and becomes sunken, dark, and leathery. On peppers, the lesion is more commonly found on the side of the fruit towards the blossom end. Also, on peppers it can be sometimes confused with sun scald. Fruit infected by blossom-end rot ripen often become infected with secondary organisms such as Alternaria spp (most likely the surrounding tissue in the photo below).
This is a physiological disorder of low calcium in the fruit. Calcium is required for normal cell growth and in relatively high concentration for new tissue growth. Rapidly growing fruit will begin to breakdown at the blossom end because that is the last place of the fruit tissue to receive calcium and also the area with the lowest concentration of calcium.
In rapidly growing plants, calcium cannot move to those rapidly growing areas quickly enough. Because calcium moves with water, fluctuations in water supply can cause blossom-end rot. Large fluctuations in soil moisture inhibit uptake and movement of calcium within the plant. Excessive nitrogen promotes rapid plant growth, which can cause low concentrations of calcium to occur in plant tissue. Leaf tissue can often not disclose a low calcium in fruit because of the lag in movement of calcium to the rapidly growing fruit tissue.
Other causes such as low calcium levels in the soil or high amounts of cations in the soil which compete with calcium uptake can also cause blossom-end rot. This is especially true in areas of soils derived from serpentine rock that are high in magnesium. The magnesium competes with calcium uptake.
Proper fertilization and water management help to minimize this problem. Avoid over fertilizing the crop. Also avoid allowing the soil to become too dry and then overly wet. Wide fluctuations in soil moisture inhibit calcium uptake and movement. If calcium is deficient or high salts occur in the soil, gypsum applications can help, but delayed uptake may not help fruit tissue content. Often, foliar applications of calcium may be beneficial.
- Author: Ben Faber
It is possible to blame a lot of things on the Drought, and here's another one. There have been reports of damaged fruit from the leaffooted bug - Leptoglossus occidentalis, although there are other species. This is a relative of stinkbugs which we have been seeing quite a number of this year. Bagrada Bug and the Brown Marmorated Stink Bug are also stink bugs.
The adults overwinter in wild areas on grasses and other hosts. Cool winters will often kill many of the adults, and in Southern California after a warm winter many survive. When the hills and surrounding areas dry up, they move to where they can find food – an orchard, a field, a backyard. They especially like fruit, which they pierce and suck, and older insects will inject an enzyme to digest the seed in the fruit. The piercing will cause a blemish to the fruit, but often it is still edible. Common fruits attacked are citrus, tomato and pomegranate. Nut crops can be heavily affected.
One of the problems with this pest is that the damage is seen long after the insect has departed, died, parasitized or predated. So, it is too late to spray. Mandarins, navels, figs and pomegranates could now be showing low level symptoms of the attack of these bugs.
Populations of these bugs fluctuate from year to year. Symptoms of damage often look like those of other stink bugs or even wind scarring. For more information see:
http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74168.html
Image top to bottom:
Damage to citrus
Eggs
Adult