- Author: Help Desk Team
Are you noticing that the leaves on your citrus trees are looking yellow, and wondering if now is the time to fertilize? We have some answers for you.
Should You Fertilize Now?
First of all, don't be too worried about the yellow leaves. The yellowing, especially the yellowing of the leaf veins, is related to a lack of nitrogen. Citrus leaves are frequently yellow in the winter due to the trees' inability to take up nitrogen in cold weather. But now, as the days get longer and the soil begins to warm, the trees are getting ready to pick up nitrogen from the soil which means we are getting closer to the start of the citrus tree fertilization process.
Citrus trees are typically fertilized at three points in the year. The first is in January or February just before the trees begin to bloom. Exactly when will depend on your microclimate and the trees' readiness. Given the climate differences In Contra Costa County, in west county, you may need to apply the first fertilizer in late January, while the trees in central and east county may not be ready until mid- to late-February.
The next application time is in May, with a third application in June if necessary. And that is it for the season. Avoid fertilizing any later in the year, since late-season fertilization can have adverse effects on the fruits, including reduced fruit quality, delayed fruit coloring, and rough rinds. Late-season fertilization can also cause off-season growth making the trees more susceptible to diseases, disorders, and pests. Frost damage and leaf miner infestations are two common problems with late-season fertilization.
What Kind of Fertilizer Should You Apply?
Nitrogen is the main nutrient that you need to provide. Contra Costa soils are typically deficient in nitrogen and citrus trees are heavy nitrogen users. There are many sources of nitrogen. An easy choice for the home gardener is an organic citrus fertilizer. Fertilizers are labeled with three numbers on the front of the package, indicating percentages of N (nitrogen), P (phosphorous) and K (potassium). Look for a fertilizer where the first number (nitrogen) is the highest of the three, e.g., 7-3-3.
Citrus can also suffer from micronutrient deficiencies including zinc or iron. Most organic fertilizers contain these micronutrients, but if the leaves on your citrus have yellow patches between green veins you may need to correct these deficiencies by applying a foliar application of a liquid chelated micronutrient solution as the new growth emerges in the spring.
You can check here on the signs of different nutrient deficiencies to get an idea of what you are dealing with: https://ipm.ucanr.edu/PMG/C107/m107bpleaftwigdis.html
No matter which product you are applying, make sure that you carefully follow all label directions on the amounts and timing of the fertilizer application. Avoid over fertilizing which can cause excessive new growth, making the trees susceptible to other disorders such as bacterial blast.
Micronutrient deficiencies can also occur if the soil is too acidic or too alkaline. Citrus trees can tolerate a pH in the range of 6.0-7.5, with 6.5 being optimum. Contra Costa soils tend to be on the higher, alkaline side. If you have taken the actions above and are still not seeing the results you want, a soil pH test may be your next step. You can use an off-the-shelf home soil test kit or send a soil sample to a commercial soil test company.
How Should You Apply the Fertilizer?
The fertilizer should be scattered evenly on the soil under the tree's canopy. Make sure that you distribute the fertilizer at least as far out as the drip line. Avoid the area near the trunk. Lightly scratch the fertilizer into the surface of the soil and then irrigate.
For more information on citrus fertilization, including guidelines on the amount of nitrogen needed based on the age of the tree, see: https://ipm.ucanr.edu/PMG/GARDEN/FRUIT/CULTURAL/citfertilization.html
For a full set of tips on growing citrus, see: http://ipm.ucanr.edu/PMG/GARDEN/FRUIT/citrus.html
We wish you the best with your citrus trees. Proper fertilization and care should provide you with healthy trees and tasty fruit.
Help Desk of the UC Master Gardener Program of Contra Costa County (ECS)
Advice for the Home Gardener from the
Help Desk of the UC Master Gardener Program
of Contra Costa County
Subject: Grapefruit Tree vs Woodpecker
Cllient's Request: How can we keep a woodpecker(s) from making holes in the tree bark? We don't have any insects/ants on the tree bark and we're concerned that the damage will make the tree susceptible to disease. Thank you.
MGCC Help Desk Response: Thank you for contacting the UC Master Gardener Program Help Desk with a question about woodpeckers on your grapefruit tree. From our phone conversation this morning, I identified the culprits as sapsuckers. These drill a series of holes, usually in straight horizontal lines, in live trees so plant sap oozes out of the holes. Sapsuckers feed on the sap, as well as on any insects that become trapped in the sap. Most of the time, sapsucker holes do not cause problems for the tree. When there is continuous sapsucker activity that increases the lines of holes to a significant percentage of the tree's trunk area, it can weaken the tree and potentially kill it.
Physical exclusion is the best way to prevent any kind of woodpecker damage. There are several methods you might see mentioned to prevent such as frightening devices or repellents, but these are not typically successful as birds quickly become accustomed to the deterrent. Covering the trunk with something that will prevent access to the tree bark is the best way to get sapsuckers to move on. Sections of lightweight sheet metal or roof flashing are fairly easy to shape around the trunk. You can get rolls of aluminum flashing at home improvement stores. Heavyweight plastic material can also be used. Use duct tape to hold it in place. You can also use wire mesh such as chicken wire, especially if it's bunched up somewhat. You will probably need to cover a great deal of the tree's bark to prevent the birds from just moving to an uncovered area. Whatever you use to cover the bark, make sure it is not too tight--you want to leave room for the tree to grow--and remove it when the birds have moved on. Depending on the size of the tree, you could also cover the entire tree with bird netting that you securely attach around the low base of the trunk to prevent all access to the tree.
Woodpeckers drill holes in trees for a variety of reasons. The largest holes are drilled for nest construction, usually in dead trees. Acorn woodpeckers drill 1/2 inch holes in which they store acorns. Smaller random holes are those made while looking for food. Woodpeckers' sharply pointed beaks and long tongues are used for extracting larvae and other insects from wood crevices. This can actually alert you to burrowing insects damaging a tree.
This link is to more information from the University of California about managing woodpeckers: http://ipm.ucanr.edu/PMG/PESTNOTES/pn74124.html.
I hope this information is helpful. Please don't hesitate to contact us again if you have more questions.
Help Desk of the UC Master Gardener Program of Contra Costa County (SEH)
Notes: Contra Costa MG's Help Desk is available almost year-round to answer your gardening questions. Except for a few holidays (e.g., last 2 weeks December), we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 2380 Bisso Lane, Concord, CA 94520. We can also be reached via telephone: (925) 608-6683, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/. MGCC Blogs can be found at http://ccmg.edu/HortCoCo/ You can also subscribe to the Biog.
Advice for the Home Gardener from the Help Desk of the
UC Master Gardener Program of Contra Costa County
UC does not have any recommendations for the home gardener to deal with this. It will likely not damage the tree, but the lemons can look pretty bad and will not keep well. The infection does not penetrate beyond the rind. As you've seen, the inside of the lemon is still good.
The best advice is to remove all the fruit once the weather has dried and to remove and dispose (i.e., green can) of any fallen leaves and fruit from around the tree. This is to remove as much of the fungal material as you can. The spores were probably on the ground and were splashed up into the tree when it rained. Add fresh mulch in that area which will help to cover up existing spores. Do this after the weather becomes dry (be sure to leave the trunk area clear of mulch by 4”). You can also thin out some of the canopy to let in more light and air, but don't prune while it is wet. Dispose of the tree pruning into the green can too. With the recommended effort hopefully, you can stop this pest and have lemons next year.
Please don't hesitate to contact us again if you have more questions.
Help Desk of the UC Master Gardener Program of Contra Costa County (SEH)
| Don't miss our 2019 Great Tomato Plant Sale - Walnut Creek 3/30, Richmond 4/6, Antioch 4/13. Click here for more information:http://ccmg.ucanr.edu/tomato/ |
Note: UC Master Gardeners Program of Contra Costa's Help Desk is available almost year-round to answer your gardening questions. Except for a few holidays (e.g., last 2 weeks December), we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 2380 Bisso Lane, Concord, CA 94520. We can also be reached via telephone: (925) 608-6683, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/. MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog.
Advice for the Home Gardener from the Help Desk of the
UC Master Gardener Program of Contra Costa County
UC MG Help Desk Response: Thank you for contacting the UC Master Gardener Program Help Desk about the problem with your citrus and also thanks for sending that great picture as it allows for a clear diagnosis. Your citrus is infected with scale – but don't worry, scale can be managed.
Scale is an insect that sucks on plant juices. Left unchecked it could cause damage to or reduce the vigor of your plant. Regarding whether the quality of your fruit will be impacted - I don't believe so. The problem with the scale on the rinds is that it is primarily unsightly. If you were going to leave the rind on for your use of the fruit then you would want to scrub the surface to remove the scale bodies..
The scale on your citrus stems and fruit is an armored scale. From your picture I am unable to identify the particular species of armored scale but that does not matter because management would be the same.
What you see residing on your plant are females and immature who do not have wings and therefore simply reside there – feeding.
Understanding the basic life cycle will help to understand the pest management practices:
Adult females produce eggs that are usually hidden under their bodies. Eggs hatch into tiny crawlers (immatures) which settle down and begin feeding within a day or two after emergence. Settled immatures may spend their entire life in the same spot without moving as they mature into adults.
Chemical treatments are most effective when the crawlers are just emerging in spring. See the link at the end of the narrative (below) for additional information on monitoring when crawlers are crawling.
Management:
Provide plants with good growing conditions and proper cultural care, especially appropriate irrigation, so they are more resistant to scale damage. You can prune off heavily infested twigs and branches, if they are limited to a few parts of small plants.
Horticultural oil is effective in spring or summer on deciduous plants when sprayed soon after most crawlers have emerged and most scales are in the young immature stage. Late spring and summer are also the times to spray avocado, citrus, and many other broadleaf evergreens. Horticultural oil kills the scales through suffocation.
Where plants can be sprayed, complete spray coverage of infested plant parts with horticultural oil at the proper time provides good control of most scales. Horticultural oils (e.g., Bonide Horticultural Oil and Monterey Horticultural Oil) are specially refined petroleum products, often called narrow-range, superior, or supreme oils.
Other non-persistent, contact sprays for garden include insecticidal soap (e.g., Safer Brand Insect Killing Soap Concentrate II), neem oil (Bayer Advanced Natria Neem Oil Concentrate, Green Light Neem, Garden Safe Brand Neem), canola oil (Bayer Advanced Natria Multi-Insect Control), and other botanical (plant-derived) oils.
Thoroughly cover with spray the plant parts where scales occur, typically on twig terminals and the underside of leaves. Follow the product label with respect to target plant, timing etc. Do not apply oil or other insecticides when it is foggy, freezing (under 32°F), hot (over 90°F), when relative humidity is above 90%, or if rain is expected in the next 24 hours. Especially at locations with hot weather, be sure plants are well irrigated before spraying foliage.
Below is a link to the UC Integrated Pest Management website that provides additional information on Scale lifecycle and management.
Armored scale do not produce honey dew (a sugar based excrement) so disregard the information about monitoring honeydew and controlling ants.
http://ipm.ucanr.edu/PMG/PESTNOTES/pn7408.html
Help Desk of the UC Master Gardener Program of Contra Costa County (EDC)
Note: UC Master Gardeners Program of Contra Costa's Help Desk is available almost year-round to answer your gardening questions. Except for a few holidays (e.g., last 2 weeks December), we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 2380 Bisso Lane, Concord, CA 94520. We can also be reached via telephone: (925) 608-6683, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/. MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog (//ucanr.edu/blogs/CCMGBlog/)
Advice for the Home Gardener from the Help Desk of the
UC Master Gardener Program of Contra Costa County
MGCC Help Desk Response: Thank you for contacting the UC Master Gardener Program Help Desk with your question about navel orange fruit splitting.
Splitting citrus fruit is a common problem, especially with navel oranges. The following link (http://anrcatalog.ucanr.edu/pdf/8038.pdf) is a short 1-1/2 page informative UC document which describes the condition, along with suggestions for resolution. Very briefly, fruit splitting is likely the result of stress to the tree, and is probably related to extreme fluctuations in temperature, humidity, soil moisture, and possibly fertilizer levels. The disorder is often caused by a combination of these factors rather than by a single cause.
Avoiding fluctuations in soil moisture (suggest adding mulch under the tree and consistent and ample water, especially during heat spells) as well as fertilizer levels throughout the growing season may help to minimize fruit split.
I hope this is helpful, please contact us again with any further questions.
Help Desk of the UC Master Gardener Program of Contra Costa County (MCW)
Note: The UC Master Gardeners Program of Contra Costa's Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523, although we will be moving this spring. We will notify you if/when that occurs. We can also be reached via telephone: (925)646-6586, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/ MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog (http://ucanr.edu/blogs/CCMGBlog/)
