Research and Sustainable Integrated Pest Management Implementation on an Organic Central Coast Cut Flower Farm to Reduce Losses From Key Pests.

Cucumber Beetle in Dahlias

Cucumber beetle was identified as a key pest for this research after qualitative observations from years past. After finding that vacuuming was not a realistic use of time, blossom bagging sensitive varieties was the primary mechanical method to reduce damage. Quickly thrips filled the bags where they were protected from their natural predators pausing bagging as the primary control. Monitoring methods were adapted to include a weekly 10-flower sample count to track thrips activity in the dahlias. Once thrips pressure receded, blossom bagging commenced on sensitive varieties. While these bags did significantly reduce losses from cucumber beetle they were also very time consuming to apply and remove. On the farm, a wider mesh netting was used to protect chrysanthemums from cucumber beetle. It was found to not result in additional thrips infestation and with less time taken per bloom.

A sunflower trap crop was planted in addition to sticky cards and lures as the biological method to reduce losses. Challenging weather at the start of season one delayed the timing of the sunflower trap crop. In year one, sticky tape was also found to catch beneficial insects in addition to predators so the grower opted to not include sticky cards in year two's design.

In designing the project, the grower estimated that losses from cucumber beetles before this research were $3,340. At that time, no formal monitoring system was in place, so that number was pure estimation. After carefully tracking losses in year one of this research, the grower found that losses had surpassed that estimation well over twofold, coming in at $8,895. The reasons for this are likely a combination of estimating 2022 losses without monitoring and shifts in growing conditions after significant el niño winter storms. 

The refined approach for managing cucumber beetle and thrips in dahlias for 2024 included a new mechanical exclusion material to allow entry of thrips' natural enemies, an adjustment to our planting strategy for the sunflower trap crop to improve the stand, and a change to our method of cucumber beetle monitoring in the trap crop to protect natural enemies.

This year (2024), the grower used a narrow gauge row netting to exclude cucumber beetles from the sensitive dahlia varieties rather than blossom bagging individual blooms, which proved time and labor-intensive and also trapped thrips in the bags and excluded their natural enemies in 2023, Orius (Minute Pirate Bug), resulting in thrips damage to blooms. The netting was a fine enough gauge to exclude cucumber beetles but large enough to allow Orius to enter. Only sensitive varieties were netted in rows. While Orius counts in Dahlia were less abundant in 2024 (due to the lack of exclusion in 2023), resulting in higher populations in the blooms, they were still present under nets in 2024 and active enough to suppress thrips populations and severity below damaging levels. Some damage from the netting was seen on the dahlia petals where the blooms touched the nets due to the zigzag  planting of the dahlias in the rows. 

In year two, the grower adjusted the planting strategy for the sunflower trap crop from direct seeding, which resulted in skimpy stands in 2023, to greenhouse plug production in 2024, which resulted in full stands and successive rows of flowering sunflowers in time with the flowering of the dahlias. To reduce natural enemy losses in the sunflower trap crop to sticky traps around lures meant for cucumber beetles, the scouter did not use the sticky traps, used only lures (replaced during the season), and swept the sunflowers for cucumber beetle counts to monitor pressure levels.

Thrips and cucumber beetle damage counts ran April - October 2024. Weekly scout counts showed decreased damage to dahlias from cucumber beetle and thrips. Individual bloom losses were counted by the harvest crews in 2023 and 2024, showing an increase in cucumber beetle damage in 2024. However, it is uncertain whether the damage was correctly identified as cucumber beetle and whether other damage from netting was included in these figures. In year three, the project will continue to rely on the crop scouter figures for consistency sake.

For year three, the grower will make some changes to the design of the insect netting structure to reduce losses from the netting itself. Dahlias will be planted in single rows providing ample space for plants to grow without risk of pressing against the net. The structure itself will be reinforced with PVC "hoops" between posts to ensure the netting can float above the blooms.

Fusarium in Lisianthus

The grower had experienced significant loss due to Fusarium in lisianthus before this research, but as a high-demand flower, it is appealing to research the potential for reducing those losses. In year one, cultural methods to increase drainage and airflow were implemented at the planting stage. Plugs were planted in tall beds with plugs planted high and reduced planting density from six inches to eight inches. A Trichoderma inoculant was intended to be used only at the plug stage but was added monthly through drip irrigation.

The much wetter than usual 2022-2023 winter in Central California delayed planting these plugs, leading to rootbound plants. Weekly rogue counts from rootbound plants were added to severity monitoring to better encapsulate the challenges Lisianthus faced in year one. Plants that did survive being rootbound were symptomatic of Fusarium despite these cultural and biological methods. Flowers were still sold selectively, but overall loss was still estimated at $568 due to fusarium. After loss from rootbound plants was estimated to be more than double that from fusarium ($1,256), it's fair to say that rootbound plants are another key pest of lisianthus and were addressed in year two.

To better identify the feasibility of growing lisianthus organically in this location, irrigation water was tested for Fusarium. A negative result determined that the last change the grower could make to reduce loss from Fusarium in year two was to plant in containers with clean media. Otherwise, the same preventative cultural methods used from the start would be implemented, along with the added monthly Trichoderma chemigation. To reduce loss from rootbound plugs, plants were to be inspected and planted within a few days of receiving them.

Year two was a significantly smaller planting of lisianthus due to the complexity and expense of container production versus field production and meant to test the economical and practical potential for disease-free lisianthus production. Purchased plugs were planted into sanitized bulb crates filled with new, clean media a few days after arrival. Trichoderma was applied 1 week via chemigation through the drip lines and again monthly during the warm growing season. The planting progressed normally until early symptoms of Fusarium began to express in July 2024. Tissue samples were taken to the lab and received a result for Fusarium avenaceum, a different species of Fusarium than was initially identified in 2022 by the Agriculture Commissioner's laboratory. The technical advisor has since learned that Fusarium contamination has been found in plugs ordered from nurseries, presenting a potential inoculum source.  

Very few rootbound plants were discovered during the growing season, and we determined that this was not a significant key pest in 2024.

Overall, the planting performed similarly to previous in-ground plantings, expressing Fusarium symptoms and being generally unsaleable due to foliage and petal discoloration and uncertain shelf life. The grower and the technical advisor have concluded that it is not feasible to effectively manage Fusarium symptoms organically in lisianthus on this farm and that the likelihood of purchased plugs being infected is very high. Growing lisianthus from seed is extremely challenging and adding that to the already expensive nature of container planting, it has been determined that this portion of the research is prematurely complete. Year three will not include lisianthus in the study.

Bacterial Blight in Zinnias

While zinnias had been a successful crop for the grower, bacterial blight was a primary cause of the premature end to their growing season. This caused it to be identified as a key pest of zinnias, and cultural and biological methods were identified to research. Like lisianthus, increasing drainage and airflow and a Trichoderma inoculant were the cultural and biological controls planned for year one. The grower would typically top zinnia beds with weed control fabric as they do with all annuals spaced at eight inches or wider. The lisianthus was never a good candidate for this fabric since most growers plant closely at around six inches. While the fabric is very helpful in controlling weeds on these long-blooming plants, it was not used. A negative effect of the fabric is that it hides the pooling of water underneath due to gopher damage to drip lines, which was hypothesized to increase the proliferation of blight. Zinnia plants were planted at a wider one-foot density, although there was some variation in how many rows per bed were used due to inconsistencies in the bed top dimensions. Plants were dipped in a Trichoderma inoculant before planting as planned, and additional monthly inoculant through the drip irrigation was added as well.

As the season progressed, another pest emerged: Sclerotinia. Weekly severity monitoring was coupled with rogue counts to quantify losses to either pest. This rogue counting also clarified that two-row beds experienced a significantly lower rate of loss from both Blight and Sclerotinia (86 plants loss from a combination of the two pests in two-row beds and 647 plants lost in three-row beds). For year two, all beds were to be planted in two rows with one-foot spacing.

After seeing significant gains in our 2023 trials, the approach for 2024 was similar to 2023. Once again zinnias were planted in an area that had no prior zinnia planting, plugs planted high in tall beds with reduced plant density, treated with a biological soil inoculant at planting and monthly throughout the growing season. The refinements we made for 2024 were to plant in all 2-row beds to encourage additional airflow to discourage Blight and Sclerotinia in the crop and limit to a single planting of zinnias. 

In 2024, the farm benefited from a shorter rainy season that allowed beds to be built and plants to be installed without rain or other delays. The bed residue was insignificant enough to minimize bed destruction during weeding. The crew kept the zinnias clear of weeds throughout the main harvest season. The high planting helped encourage drainage and kept water from pooling at the base of the stems. As the plants grew, their height and the high planting caused some plants to fall into the furrows. Tricoderma was applied to the zinnias every month for three months. This was one treatment more than 2023. This was meant to inoculate the soil with beneficial bacteria that may protect the plants' roots from Blight during increased pressure from high temperatures.

Overall, there were fewer losses to Blight and Sclerotinia in 2024. However, 2-row planting may have increased losses to fallen plants due to lack of stability from other surrounding plants. Plants were not trellised, and some losses were associated with fallen plants.

For 2025, the grower will continue planting the zinnias in 2-row beds, planting plugs high in tall beds, using a biological soil inoculant treatment at planting and monthly throughout the growing season, and rotating into an area not previously planted in Zinnias. They may consider using one additional biological material to suppress Sclerotinia in the late part of the season when environmental conditions favor the disease. The grower may also consider early trellising in the zinnias to minimize losses from fallen plants while maintaining airflow in the canopy.