- Author: Kathy Keatley Garvey
Senior scientist Arnon Dag of the Agricultural Research Organization, Volcani Institute, Israel, will discuss his research at the UC Davis Department of Entomology and Nematology seminar at 4:10 p.m., Monday, Nov. 27 in 122 Briggs Hall.
His seminar, titled "Improving Cross-Pollination in Deciduous Fruit Trees," also will be on Zoom: The Zoom link:
https://ucdavis.zoom.us/j/95882849672.
"Tree crops belonging to the Rosaceae, such as almond, pear, apple, and sweet cherry, depend on cross-pollination by insects to set fruit," Dag says in his abstract. "The primary pollinator of the crops is the honey bee (Apis mellifera). However, due to harsh climatic conditions during flowering, limited movement of bees between cultivars, low preference of the bees for flowers of the target crop, and limited overlap in flowering between the cultivars, pollination is a primary factor limiting yield. Our group has tested multiple approaches to mitigate this problem: Using 'Pollen dispensers,' sequential introduction of beehives to the orchards, selection of honeybee strains with higher preference for the target crop, introduction of bumblebee (Bombus terrestris) colonies and phosphorous fertilization to increase nectar secretion and improve crop-flower attractiveness. I will summarize the effects of those methods on fruit set and yield in apples, almonds, and pears."
A native of Moshav Lachish, Israel, Dag received his bachelor's degree (1990) and master's degree (1992) in life sciences at the Faculty of Life Sciences, Tel Aviv University. His master's thesis: "Improving the Honey Bee Efficiency of Melon Pollination in Greenhouses." He obtained his doctorate in agriculture at the Horticulture, Faculty of Agriculture at Hebrew University of Jerusalem, completing his dissertation on "Pollenizers, Pollinators and Pollination in Mango." He held postdoctoral positions at both Tel Aviv University and the Hebrew University of Jerusalem.
Dag's research interests include fruit tree physiology, olive biology and cultivation, reproductive biology of fruit trees, crop pollination, pomology in semi-arid conditions and "developing guava as an export crop."
He served as an Extension specialist in beekeeping from 1991 to 2003 for the Israeli Ministry of Agriculture.
Seminar coordinator is Brian Johnson, associate professor, UC Davis Department of Entomology and Nematology. For Zoom technical issues, he may be reached at brnjohnson@ucdavis.edu. The list of seminars is posted here.
- Author: Anne Schellman
What is a Deciduous Fruit tree?
Deciduous fruit trees lose their leaves in fall, and include apple, pear, fig, pomegranate, nectarine, cherry, apricot, peach, and plum.
Planting New Trees & Understanding Where Fruit Originates
Sometimes a fruit tree mysteriously dies, and the gardener isn't sure what happened. A common cause is a tree that was planted too deeply. Root and crown rot slowly affect the tree, causing it to die years later. Watch the detailed instructions on how to plant correctly.
It's important to understand how new fruit develops and grows on the tree. Not all deciduous fruit trees produce fruit in the same place. It's important to know this so you don't accidentally cut off fruit spurs and damage your tree's ability to produce fruit. See this video for guidance. https://www.youtube.com/watch?v=-4fgVrf8XHE&t=250s
Publication - Fruit Trees: Planting and Care of Young Trees https://anrcatalog.ucanr.edu/Details.aspx?itemNo=8048
Fruit Trees: Training and Pruning Deciduous Trees https://anrcatalog.ucanr.edu/Details.aspx?itemNo=8057
Keeping New Trees Small – the Fruit Bush Method
Tired of out-of-control fruit trees? If you are planting a new tree, watch this video! It details the Fruit Bush Method, a specific way of keeping fruit trees small. See photos of 5-6' tall fruit trees planted over 30 years ago that continue to produce an ample amount of fruit. https://www.youtube.com/watch?v=ry4YAp6NzdI&t=1s
Pruning Established Trees
Other Helpful Publications
Fruit Trees: Thinning Young Fruit https://anrcatalog.ucanr.edu/Details.aspx?itemNo=8047
What about Citrus Trees?
Citrus trees such as oranges, lemons, grapefruits, lime, and kumquats are evergreen trees and need different care than deciduous trees. It's not recommended to prune citrus trees at the same time as deciduous fruit trees. Wait until spring to prune your tree for size and shape.
We are offering an online class on citrus on January 31, so watch for our registration advertisement in about a week. Locally, we will be teaching at 8 library locations about citrus during March.
/h3>/h3>/h3>/h3>/h3>/h3>Life Cycle
Most aphids in California's mild climate reproduce asexually throughout most or all year with adult females giving birth to live offspring—often as many as 12 per day—without mating. Some species produce sexual forms that mate and produce eggs in fall or winter, providing a hardier stage to survive harsh weather and the absence of foliage on deciduous plants. When the weather is warm, many species of aphids can develop from newborn nymph to reproducing adult in seven to eight days. Because each adult aphid can produce up to 80 offspring in a matter of a week, aphid populations can increase with great speed.
Damage
The aphid sucks out the juice from the leaves, damages the young shoots and leaves behind a sticky sweet substance (honeydew) that attracts ants. After they're done, the leaves turn yellow, twist and die. The leaves are left with dark spots, plaque and mold. Aphids on apple tree seedlings cause twigs to wither and stop growth development. However, they seldom kill a mature plant.
Monitor
Check your plants regularly for aphids—at least twice a week when plants are growing rapidly—in order to catch infestations early, so you can knock or hose them off or prune them out. Many species of aphids cause the greatest damage in late spring when temperatures are warm but not hot (65°-80°F). For aphids that cause leaves to curl, once aphid numbers are high and they have begun to distort leaves, it's often difficult to control these pests, because the curled leaves shelter aphids from insecticides and natural enemies.
Ants are often associated with aphid populations, especially on trees and shrubs, and frequently are a clue that an aphid infestation is present. If you see large numbers of ants climbing your tree trunks, check higher up the tree for aphids or other honeydew-producing insects that might be on limbs and leaves. To protect their food source, ants ward off many predators and parasites of aphids. Managing ants is a key component of aphid management.
Natural enemies can be very important for controlling aphids. Many predators feed on aphids. The most well-known are lady beetle adults and larvae, lacewing larvae, soldier beetles, and fly larvae. Naturally occurring predators work best, especially in garden and landscape situations. Applying commercially available lady beetles (the convergent lady beetle, Hippodamia convergens) may give some temporary control when properly handled, although most of them will disperse from your yard within a few days.
Among the most important natural enemies are various species of parasitic wasps that lay their eggs inside aphids. The skin of the parasitized aphid turns crusty and golden brown, a form called a mummy. The generation time of most parasites is quite short when the weather is warm, so once you begin to see mummies on your plants, the aphid population is likely to be reduced substantially within a week or two.
In some situations, ants tend aphids and feed on the honeydew aphids excrete. At the same time, ants protect the aphids from natural enemies. If you see ants crawling up aphid-infested trees or woody
plants, put a band of sticky material (e.g., Tanglefoot) around the trunk to prevent ants from climbing up. Prune out other ant routes such as branches touching buildings, the ground, or other trees.
Cultural Control
Where aphid populations are localized on a few curled leaves or new shoots, the best control may be to prune out these areas and dispose of them. In large trees, some aphids thrive in the dense inner canopy; pruning out these areas can make the habitat less suitable.
High levels of nitrogen fertilizer favor aphid reproduction, so never use more nitrogen than necessary. Instead, use a less soluble form of nitrogen and apply it in small portions throughout the season rather than all at once. Slow-release fertilizers such as organic fertilizers or urea-based time-release formulations are best.
When considering whether to apply insecticides for aphid control, remember that most larger plants can tolerate light to moderate levels of aphids with little damage. Larger aphid populations often rapidly decline due to biological control or when hot temperatures arrive. Often a forceful spray of water or water-soap solution, even on large street trees, when applied with appropriate equipment, will provide enough control.
If insecticides are needed, insecticidal soaps and oils are the best choices for most situations. Oils may include petroleum-based horticultural oils or plant-derived oils such as neem or canola oil. These products kill primarily by smothering the aphid, so thorough coverage of infested foliage is required. Apply these materials with a high volume of water, usually a 1 to 2% oil solution in water, and target the underside of leaves as well as the top. Soaps, neem oil, and horticultural oil kill only aphids present on the day they are sprayed, so applications may need to be repeated. Although these materials can kill some natural enemies that are present on the plant and hit by the spray, they leave no toxic residue, so they don't kill natural enemies that migrate in after the spray.
Also, don't use soaps or oils on water-stressed plants or when the temperature exceeds 90°F. These materials may be phytotoxic to some plants, so check labels and test the materials on a portion of the foliage several days before applying a full treatment.
Supreme- or superior-type oils will kill overwintering eggs of aphids on fruit trees if applied as a delayed-dormant application just as eggs are beginning to hatch in early spring. These treatments won't give complete control of aphids and probably aren't justified for aphid control alone but will also control soft scale insects if they are a problem. Common aphid species controlled with these types of oils include the woolly apple aphid, green apple aphid, rosy apple aphid, mealy plum aphid, and black cherry aphid.
References Aphid Management Guidelines, UC IPM. http://ipm.ucanr.edu/PMG/PESTNOTES/pn7404.html
Aphids in Gardens and Landscapes: Quick Tips. http://ipm.ucanr.edu/QT/aphidscard.html
- Author: Ben Faber
That's a good question. Some question whether they flourish now. Southern California does not have the landscapes of apples, pears and peaches of Oregon, Michigan, Pennsylvania or even Fresno, but there are nice little niches of persimmon, low chill apple, and even blueberries that thrive in the lower winter chilling environments along the coast and in the south of California.
Here is an example of what might happen to this fruit industry here. A recent, detailed study extrapolate the accumulation of cold periods in Spain over the next 30 years and to the end of the century. This provides growers with important information on the viability of future fruit cultivation in the various Spanish regions, as it allows them to know if there will be the necessary accumulated cold for the fruits to grow correctly or if they should relocate their crops to other areas.
The results obtained show a general reduction in the accumulation of cold in any future period for all the chilling models and scenarios considered. The reduction is especially significant at the end of the century, under the most pessimistic scenario. These results invite us to strongly commit, not only to adapt but also to mitigate climate change, something that would make an important difference. The probable reduction of cold would threaten the viability of some varieties of fruit trees in the near future, especially in regions where there is currently a low accumulation of cold and there are varieties that require a lot of it.
The study can be viewed at:
https://www.nat-hazards-earth-syst-sci.net/19/1087/2019/
Climate change discussions for California can be found at these websites:
https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=30513
https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=28175
An intriguing Santa Barbara apple study grower's observations are worth noting: https://ucanr.edu/blogs/Topics/index.cfm?start=1&tagname=apples
By the way the 'Moor Park' apricot is not from Moorpark, CA, but from England and the variety has never done very well in Moorpark (http://www.ngr.ucdavis.edu/treedetails.cfm?v=997).
- Author: Ben Faber
It seems the humble earwig that can cause so much damage in citrus orchards in some years on some small trees can be a great boon in biocontrol. Read on:
WSU scientists unmask the humble earwig as an apple-protecting predator
By Seth Truscott,
College of Agricultural, Human, and Natural Resource Sciences
https://news.wsu.edu/2019/06/05/wsu-scientists-unmask-humble-earwig-apple-protecting-predator/
Helping Northwest apple growers protect their crops, WSU scientists have found new proof that earwigs are actually valuable predators in apple orchards, rather than the creepy, crawly, apple‑damaging pests they're sometimes assumed to be.
In the May 2019 edition of the journal Biological Control, Robert Orpet, recent doctoral graduate at Washington State University's Tree Fruit Research and Extension Center, details findings from his multi‑year effort to shed light on the European earwig and its role in combating a costly orchard pest.
“Earwigs will eat just about anything, but we've found that aphid pests are high on their menu,” Orpet said. “By dining on pests and reducing growers' need to spray insecticides, earwigs are unappreciated predators that have important benefits for agriculture.”
Shy, invasive omnivore
An invader in U.S. orchards and gardens, the European earwig was first found in Seattle in 1907, spreading across the continent soon after. With their wriggly bodies and scary‑looking tail pincers, earwigs have always suffered from a bad reputation.
“Apple pickers don't like them, because they have a tendency to hide in apple clusters,” Orpet said. “Farmers often find them inside damaged fruit, and since earwigs feed mostly at night, it's hard to see what they feed on. “Some growers wonder if they cause damage themselves.”
Scientists like Orpet, however, have long suspected that earwigs are an important predator of aphid pests.
Apple trees covered in “snow”
Orpet came to the earwig through his research into the woolly apple aphid, a costly pest of Washington's $2.4 billion apple industry.
Gaining its name from their coat of cottony fibers, woolly apple aphids feed on the roots and branches of apple trees, stealing nutrients and water and causing galls, or abnormal growths. Infestations can decrease tree growth and keep fruit from developing, while the aphid's sticky honeydew secretions can bring on fungal infections.
About the size of a sesame seed, woolly apple aphids can amass in fluffy, meter‑long colonies.
“In bad years, infestations make apple trees look like they're covered in snow,” Orpet said. “That's when growers really take notice.”
Growers have difficulty managing woolly aphids with insecticides, because there are few effective insecticides, and no organic ones, currently available. Well‑known predators like ladybugs and lacewings could take a bite out of the woolly aphid population, but Orpet wanted to know if the earwig makes a difference.
Working with Jessica Goldberger, an agricultural sociologist at WSU's Department of Crop and Soil Sciences, Orpet interviewed 15 orchardists and managers in Washington state, gauging their opinions on the insect's role.
Most growers weren't sure whether earwigs make a real difference for their crops, and some thought of them as minor pests.
At the same time, Orpet was learning what earwigs are really up to in Washington orchards. Working with managers at four different commercial orchards, Orpet set about catching earwigs with cardboard traps.
Aphids: Earwigs' favorite food
Active at night, earwigs hide by day in tight spaces. Corrugated cardboard sheets are a perfect shelter, so he could easily shake them out and count them.
Sectioning off orchards, Orpet removed earwigs in some places, adding them at others. In every site, he counted woolly aphid colonies and checked for fruit damage.
“There was an obvious difference,” Orpet said. “There were fewer aphid colonies in places where I released earwigs.” He found no evidence that earwigs were causing damage themselves, but captured video footage of earwigs eating aphids and destroying their colonies.
Orpet also inspected the contents of trapped earwigs' digestive systems to see what they actually eat. He found that earwigs regularly dine on aphids, even when local aphid populations are small.
“Our results show that earwigs aren't pests, and actually improve biological control,” Orpet said. “Some farmers spray chemicals to knock down their populations, but this research shows they don't have to, and probably shouldn't.
“Growers can reduce pesticide use, save on chemicals and labor, and leave this misunderstood predator to do its beneficial work, protecting their apples from aphids,” he added.
Along with Orpet and Goldberger, co‑authors include WSU entomology professors David Crowder and Vince Jones.
Their research was funded by the Washington Tree Fruit Research Commission, USDA's National Institute of Food and Agriculture, and the Western Sustainable Agriculture Research and Education Program.
Media contact:
- Robert Orpet, doctoral graduate, Department of Entomology, 847‑337‑4480, robert.orpet@wsu.edu