California and Arizona citrus nursery growers are shifting production of critical plants from the outdoors to ‘indoor protective structures’ to gain protection from the Asian citrus psyllid (ACP) insect and its primary vectored disease Huanglongbing (HLB).
ACP and HLB are major threats to the U.S. citrus industry. The ACP was first found in California in August 2008 and in Arizona in October 2009. Neither state has HLB, a disease which kills every tree it infects.
Growing plants indoors is much different than outdoor production, says Jim Bethke, University of California Cooperative Extension floriculture farm advisor in San Diego County.
“The plants change, the pests change, and the soil and growing environment changes.”
Bethke has spent decades helping San Diego County ornamental plant growers successfully farm plants in greenhouses. He shared his experiences and what citrus nursery growers could experience in indoor production during the “Life on the Inside” citrus nursery workshop in Ontario, Calif., in mid August, sponsored by the California Citrus Nursery Board.
One of the first realities of growing plants indoors is the pest complex can increase.
“You’ll likely find extra pests indoors that you haven’t dealt with outside including mites and thrips,” Bethke told the citrus nursery crowd. “It’s very hard to exclude mites with screening material. The screen can exclude the Asian citrus psyllid, but will not keep out thrips.”
For decades, pesticide applications in greenhouses have typically followed a calendar schedule. Ornamental plant growers are keenly aware that mites and aphids show up in the spring and leafminers appear closer to summer. Pesticides were applied whether the pest was present or not.
The more recent trend in greenhouse production is reduced pesticide use due to integrated pest management (IPM) strategies plus effective pest monitoring and scouting.
“A lot of time and effort is spent looking for pests and positively identifying the pests,” Bethke said. “Every effort is made to control pests before pesticides are ever applied.”
A knowledgeable staff is critical to this success and in a small operation staffing may include strictly the owner.
In larger operations with multiple employees, Bethke recommends a three-member team – one member each to focus on IPM, decision making, and plant production. The team should meet on a regular basis.
“The IPM team should closely monitor plants for pests and then record and summarize the information on paper,” Bethke said.
The scout monitors for pests and the decision maker decides if the pest has reached a level that requires a control measure. The grower, the most familiar with the crop, walks the crop on a daily basis and can identify problems with the plants. These three working together can make good decisions on needed pest control.
Pest sampling crucial
Pest sampling is crucial to understanding the exact pest population in the greenhouse.
Indirect sampling can include yellow sticky traps, pheromone traps, and blacklight traps. Bethke recommends at least one sticky trap per every 10,000 square feet. One trap per every 1,000 square feet is best. Position the traps vertically above the crop.
“One trap per 1,000 square feet is recommended when a serious pest problem exists or the crop is sensitive to pests,” Bethke explained. “This more expensive but is much more effective at catching a serious problem in the greenhouse.”
Traps do not provide data on immature pest populations and disease, Bethke says. Insects are attracted to the color yellow and are drawn to the yellow traps. Insects are attracted to plants since green plants contain a heavy yellow pigment.
Direct pest sampling is the most precise way to determine actual pest thresholds. Bethke recommends examining plant or leaf samples, turning the leaf over for inspection since insects tend to hide on the back side, and observational counting by walking down the plant row.
Direct sampling should include optivisor or a hand lens to examine the leaf for pests. Bethke recommends further examination under a microscope. Positive pest identification is the key to proper pesticide control and determines if pests have been killed by the treatment applications.
Other effective direct sampling techniques include tapping the plant to knock insects onto a sheet of white paper for examination. On large trees, hitting the limbs can knock off pests for gathering.
With both plant sampling methods, Bethke recommends scouting the entire area in a consistent, uniform manner - inspecting several plants from various locations. Target pest hot spots near vents, doors, edges, warmer areas, and more susceptible plant cultivars. Then flag the hot spots.
Treating the entire structure with pesticide may not be necessary.
“It doesn’t make sense to treat the entire facility if the pests are only at a corner of the greenhouse or near a door,” Bethke said. “Treating only the hot spots saves time plus pesticide and labor costs.”
Written records should include the number of plants inspected, damage or infestation, specific pest species and abundance, exact pest locations, environmental conditions, the time involved to scout and apply control measures, and control costs.
Pest monitoring has many benefits including: precise pest site locations, evaluation of control measures, collecting data over time which helps predict future pest populations, reduced pesticide resistance, lower pesticide exposure to workers, improved plant growth, and increased profit by reducing pesticide costs.
Pesticides are expensive and should only be used when needed.
“Pesticides are not always needed and should be only used when necessary using the correct product for the correct pest at the correct developmental stage for a specifically identified pest,” Bethke said. “Follow the label. If you apply at a higher label rate you’ll have a greater chance of developing insecticide resistance.”
Pesticides can fail to control pests but usually the real culprit is human error. The most common human mistakes include the failure to implement an IPM program, a failure to monitor, misidentification of pests, incorrect pesticide application rates, pesticide resistance, and using old products.
“Some growers have a cabinet of old pesticide materials. These products will not work,” Bethke said. “Pesticides stored in hot areas degrade over time.”
Another reason pesticides fail is due to the water used in tank mixes. “Water is huge,” Bethke said. “Most pesticides work better if the water is acidic.”
Greenhouse plant production incorporates many plants grown in tight quarters. It is more difficult to effectively cover plants with pesticides. A successful tool to improve pesticide performance is the use of adjuvants.
“Insecticides, including the product Abamectin for mite control, work better and for a longer period of time with an adjuvant,” Bethke said.
Adjuvants can enhance the consistency of pesticides thereby reducing pesticide roll off from the plant to the floor.
Another reality of greenhouse farming is insects mature faster due to higher temperatures in the facility.
Bethke also stressed the importance of pesticide rotation to reduce pest resistance by using various modes of action (MOA). MOA information is available from the Insecticide Resistance Action Committee online at www.irac-online.org.