PLANTS THAT PRODUCE

Plants That Produce

Citrus, The Beleaguered Fruit

By Richard Frost

It’s disgusting when people smuggle plants and fruits across a state or international border just to save money. The plant they are smuggling could be harboring pests that harm not only that plant but also completely different and unrelated plants. Basically, they are putting entire agricultural crops at risk for their own personal gain. Buying your plants from a local certified nursery is better for both your local economy and your local environment.

Plant pests and diseases can be a complicated affair, and this is true for Citrus. Native to the Chinese mainland, its tissues and fruits can be a scrumptious treat for insects and critters native to our area. When under stress or attack, Citrus plants excrete a defensive serum on their leaves which is unfortunately attractive to some local pests and well-suited for black mildew and other local fungi. You can control this by washing your plants off at most once per month with a 1 tablespoon/gallon solution of sodium-free baking powder (potassium bicarbonate). Wash, don’t water the plants with it – the solution is alkaline.

In addition to local pests such as aphids, there are 3 exotic pests brought in by smugglers that affect Citrus. First, there is the Mediterranean Fruit Fly (aka Med-fly) which breeds at astronomical rates in the fruits of many plants, including chili peppers! Second, there is the Citrus Leaf Miner that causes deformation in new Citrus leaves. There are only two effective treatments for this pest (1) Spinosad, a bacterial solution that penetrates the leaves and kills the larvae or (2) a systemic pesticide labeled for Citrus – which in California you will need a pesticide applicators license. Third, we have the insidious Asian Citrus Psyllid (ACP). This pest can carry a bacterial disease called Huanglongbing, aka HLB or “Citrus Greening”. As of this writing, the ACP insects detected in southern California do not have the disease. However, it has been devastating in the southern U.S. killing over half of the agricultural citrus trees in the states of Georgia and Florida. Citrus plants and fruit in southern California are under quarantine and cannot be legally moved unless treated by a certified pesticide applicator. Also due to the ACP treatments, no Citrus fruit grown in the southern California quarantine area can be legally sold as “certified organic”. For more information on these pests, please see www.cdfa.ca.gov/phpps/.

April through September is an excellent time to plant Citrus in San Diego so let’s talk a bit about the plants themselves. As many of you know, a “dwarf Citrus” is not a short plant but instead a fruiting variety that has been grafted on top of a specific root body which causes it to grow more slowly. This is fine for backyard Lemons, Grapefruits, and Oranges but a poor idea for Kumquat, Lime, and Mandarins (aka Tangerines). They are smaller plants to begin with and do not need “dwarfing” in our local calciferous and/or clay soils – or even in large containers. When planting in the ground, be sure to excavate at least a 3 x 2 x 2 cubic foot hole to loosen the soil and make sure water will drain from it. For varieties, I recommend Normann Seedless Kumquat, Bearss Lime, Gold Nugget Mandarin (Tangerine), Washington or Cara Cara Naval Orange, Eureka Lemon, Oroblanco Grapefruit, plus several less-common types documented at www.PlantsThatProduce.com/guides/CommonCitrus.htm.

SDHS member Richard Frost is a certified edible gardening nut. For copies of past articles and more information, please see www.PlantsThatProduce.com.

Reprinted with permission from April 2010 "Let's Talk Plants," the newsletter of the San Diego Horticultural Society, www.sdhortsoc.org