2012 Winter – Research Updates

Using Flowers to Attract Beneficial Insects in Field Crops

Researchers at the University of California are investigating the use of interplanting agronomic food crops with harvestable floral crops, including cut flowers and herbs. The purpose of these plantings is to provide nectar and pollen to promote the establishment of beneficial insect populations that will  control pests on the food crop. This project specifically looked at the population of hoverflies, a highly effective predator of aphids.

There are several considerations for selecting a suitable flowering species. For example, flowering plants vary widely in their attractiveness to beneficial insects, so screening may be necessary to determine whether a flower species and an insect species are compatible. Also, the flowering plant will ideally bloom early enough in the crop cycle to attract natural enemies before pest damage occurs on the agronomic crop.

The agronomic crop for this study was kale, while the floral species were: sweet alyssum, buckwheat, tansy phacelia, wild mustard, wild arugula, Thai basil, white borage, cosmos and nasturtium. Sweet alyssum, buckwheat and tansy phacelia are commonly-used insectary plants. Wild mustard, wild arugula and Thai basil are edible herbs, and white borage, cosmos and nasturtium have value as cut flowers. The criteria for selection were:

Annual growth cycle and fast growth
Ability to start from seed
General hardiness
Tolerance of full sun
High level of flower production
Marketability of the harvestable floral species

After observing insect populations (pest and beneficial) on the kale and the floral species, this study found sweet alyssum to be the superior attractant for hoverflies. Sweet alyssum also bloomed early and continuously. Herbs may not be a viable “harvestable floral crop” since most are not marketable if allowed to flower and the stems become woody at flowering. The cut flowers would need to be harvested at bud stage or young flower, therefore not maximizing the support of beneficial insects. However, harvesting some, not all, of the cut flowers could be a mutually beneficial solution. Testing more species, including some perennials, and planting combinations of floral crops were identified as areas for further research.

Hogg, B.N., R.L. Bugg, K.M. Daane. 2011. Attractiveness of common insectary and harvestable floral resources to beneficial insects, Biological Control, pp. 76-84.

Hot Water Treatment for Asiatic Lilies

Leaf yellowing in Asiatic lilies can limit the vase life of harvested stems. Some methods used to avoid leaf yellowing include hormone-based foliar sprays and pretreatment with 1-MCP. This research, conducted in New Zealand, looked at the use of postharvest hot water treatments (HWTs) as an alternative non-chemical means to prevent leaf yellowing in Asiatic lilies.

The study concluded that postharvest HWT can delay leaf yellowing and decrease incidence and severity of leaf senescence in Asiatic lilies. The optimal treatment protocol tested was between 50C (122F) for 5 minutes and 52C (125.6F) for 2.5 minutes. Using the right combination of temperature and time was an important factor to avoid heat damage such as pitting of the leaf surface. Dipping the flowers buds resulted in abnormal flower opening. Vase life was increased by 3 days for stems treated with a hot water dip. The only cultivars evaluated were ‘Elite’ and ‘Cordelia’, therefore, further evaluation of additional cultivars was recommended for further research.

Woolf, A.B., S. Combes, M. Petley, S.R. Olsson, M. Wohlers, R.C. Jackman. 2012. Hot water treatments reduce leaf yellowing and extend vase life of Asiatic hybrid lilies, Postharvest Biology and Technology, pp. 9-18.

Controlling Corm Rot and Vascular Wilt in Gladiolus with Rhizobacterial Mix

Corm rot and vascular wilt of gladiolus cause substantial yield loss to the long-duration gladiolus crop. Quality and quantity of spikes and corms are reduced by these diseases. Control of Fusarium oxysporum f. sp. gladioli, which causes corm rot and vascular wilt, has not been fully successful using current practices. Biocontrol using plant growth promoting rhizobacteria (PGPR) is a possible alternative disease management approach. This study looked at the biocontrol efficacy and plant growth promoting activity of carrier based formulation under green-house and field conditions.

The research demonstrated that application of a talc-based formulation of a PGPR strain mixture as corm dressing and soil application reduced the incidence of corm rot and vascular wilt of gladiolus. The strain mixture also improved corm and cormel production and promoted flowering.

The study concluded that development of stable formulations of biocontrol agents will be important for gladiolus production where soil rotation is limited and fungicide use is avoided or unaffordable. The talc-based formulation of the rhizobacterial strain mixture used in this experiment has potential application in an integrated disease management program.

Shanmugam, V., N. Kanoujia, M. Singh, S. Singh, R. Prasad. 2011. Biocontrol of vascular wilt and corm rot of gladiolus caused by Fusarium oxysporum f. sp. gladioli using plant growth promoting rhizobacterial mixture. Crop Protection, pp. 807-813.