NEWSLETTER ARTICLES

Vegetables and Plant Pathology

REVIEW OF NEW INSECTICIDES UNDER FIELD DEVELOPMENT FOR VEGETABLES
by Franklin Laemmlen

The number of effective insecticides currently available for insect control in vegetables is relatively small compared with other crops. Furthermore, with the uncertainty surrounding the recent passage of the Food Quality Protection Act, as well as increasing environmental concerns, the vegetable industry in the western U.S. could potentially be facing the loss of a number of important insecticides. Consequently, there is speculation that some of the more broadly toxic compounds may be removed from the market in the next few years, and the organophosphate and carbamate insecticides are being targeted as prime candidates for reduced usage. As these older chemicals are lost, the introduction of replacement products that can live up to both regulatory and grower standards will be critical. Fortunately, there are several new insecticides currently being tested under experimental conditions, that offer excellent activity on many of the key pests that infest vegetables.

Over the past several years, whiteflies and aphids have not been a significant problem to growers, largely because of the development of Admire. Similarly, the new insecticides now being developed by the agrichemical industry have demonstrated good activity on the lepidopterous pests (beet armyworms, cabbage looper) and leafminers. Most recently, new products are being developed for control of thrips and aphids with demonstrable efficacy. In most cases, these insecticides are only a few years away from registration on leafy vegetables. The performance of these products on vegetables has in some instances not been thoroughly investigated. How they will fit into the growers’ IPM programs is not yet certain. This document was created to provide you with an overview of new insecticide chemistries being developed by the agrichemical industry for use in vegetables. The tabular information presented below is a summary of the efficacy and activity of several of these new compounds.

The first part of this report concisely describes the new types of chemistries being developed by industry. The descriptions list the new and existing chemistries (in bold) based on the most current information available to the public. Under each category are listed the individual compounds that have been tested. All insecticide compounds listed in this review are identified by their common name (italicized and lower case), trade names (if available, are shown in upper case) or code letter/number which identifies a compound in early development.

I. Conventional Chemistries: Carbamates (APHISTAR, triazimate; MESUROL, methiocarb). These products belong to the carbamate chemistry which has been developed for over 40 years. They are neurotoxic and similar to organophosphates in that they inhibit cholinesterase. Methiocarb is best known for slug and snail control in ornamentals, as well as for bird repellency. It has a federal label for control of aphids and mites in ornamentals. Triazimate is a potent systemic aphicide that is highly selective and relatively fast acting. It is mobile within the plant and is safe towards beneficial insects.

II. Novel Insecticide Chemistries: Chloronicotinyls (ADMIRE, PROVADO, imidacloprid; NI-25, acetamiprid; CGA 293343): This class of neurotoxic compounds has a mode of action similar to nicotine, and is highly effective systemically against sucking pests. Imidacloprid is most effective on aphids and whiteflies through root uptake, but does have translaminar and contact activity as a foliar spray. Acetamiprid is a new insecticide being developed by Rhône-Poulenc that is more broad spectrum with both contact and systemic activity via foliar application. CGA 293343 is a new insecticide being developed by Novartis that is systemic in the plant by root uptake and transport in the xylem. It is supposedly more mobile in the soil than imidacloprid.

Pyrroles (ALERT, chlorfenapyr): The pyrroles are compounds that act as metabolic toxins and work by uncoupling oxidative phosphorylation in the mitochondria. They have translaminar activity, and are toxic both by contact and ingestion to chewing and sucking arthropods. A Section 3 label on cotton is presently pending.

Pyridazinone (SANMITE, pyridaben): This compound is a non-systemic acaricide and insecticide that is a metabolic toxin acting as a mitochondrial Site I uncoupler. It is relatively selective on mites, aphids, and whiteflies. It presently is registered for use on apples and citrus.

Phenyl pyrazoles (REGENT, fipronil): A broad spectrum neurotoxin that works as a GABA agonist. It has contact active on both chewing and sucking insects. It has shown excellent potential for lygus bug on cotton and thrips in vegetables. It is currently registered for use in the Ag/Vet market.

Amino triazinones (FULFILL, pymetrozine): A highly selective, anti-feeding compound with a unique mode of action, acting specifically on the salivary pump of sucking insects, causing rapid cessation of feeding. It is slow-acting, but has both contact and systemic activity on aphids and whiteflies.

III. Insect Growth Regulators (IGR): Non-traditional IGRs (APPLAUD, buprofezin): A thiadizine-like compound with long residual activity that acts as a chitin synthesis inhibitor. The product has both contact and vapor activity and is primarily active against some sucking insects.

Hormone Analog IGRs: (CONFIRM, tebufenizode; NEEMIX, azadirachtin, STERLING, fenoxycarb, KNACK, pyriproxyfen): These compounds are active through the disruption of insect hormonal systems, such as the ecdysone, and juvenile hormone mediated processes that govern metamorphosis in insects. They are very selective and generally slow acting. Tebufenozide is an ecdysone agonist that inhibits molting with selective activity against lepidopterous larvae. It is easy on beneficial insects. Azadirachtin is a naturally occurring botanical that acts as an analog of ecdysone with some activity against a wide range of pests. It is currently registered as NEEMIX for use on vegetables. Fenoxycarb is a non-neurotoxic carbamate which affects the molting process. It is being developed as a companion with pymetrozine and will be labeled as STERLING for whitefly control in the U.S. Pyriproxyfen is a selective juvenile hormone analog active by suppressing embryogenesis of females and interrupting normal metamorphosis of whiteflies. It currently has a Section 18 registration for California and Arizona on cotton.

IV. Biological Pesticides: Bacterial insecticides (Bt’s): New strains of Bt are still being discovered that have activity against key vegetable pests. New toxin genes such as Cry IH, Cry IJ, and Cry IK are being developed by several companies. A new strain of B.t. aizawai (Serotype H7) was recently released as XENTARI with increased activity against Spodoptera. Most recently, a new Bt active against armyworm and looper, CRYMAX, was developed from genetically recombined strains of B.t. kurstaki.

Fungal insecticides (Beauveria bassiana): There are several species of fungi that are pathogenic against insects that have been investigated in vegetable crops. Many of them are still years away from commercial development. MYCOTROL, NATURALIS-L (Beauveria bassiana) are products recently registered on vegetables that have selective activity on aphids and whiteflies. The fungal spores need to come in direct contact with the target pest and require moderate to high levels of relative humidity to be efficacious in the field.

V. Natural Products: Botanicals (NEEMIX, azadirachtin): This IGR (see above) is derived from seed of the neem tree.

Fermentation Products (SUCCESS, spinosad; PROCLAIM, emamectin benzoate): Spinosad is a neurotoxic compound produced through a fermentation process by the naturally occurring soil bacterium Saccaroplyspora spinosa. It has translaminar activity on lepidopterous larvae and leafminers on vegetables. Emamectin is an avermectin (Agrimek) analogue that is derived from the naturally occurring soil microorganism, Streptomyces avermitilis. It is also a neurotoxin that has translaminar activity primarily against lepidopterous larvae.

VI. Transgenic Crops
Advances have been made to develop genetically altered vegetable crops with insect resistance to pests (e.g., B.t. potato, B.t. sweet corn). However, vegetable varieties for field evaluation have not been released as yet. Other transgenic toxins are also being developed, as well as herbicide-tolerant and virus-resistant vegetable varieties.

The second part of this report lists individual compounds and a summary of their chemical attributes. In addition, I have attempted to provide a general rating of their efficacy as related to commercially available standards.

Table 1. Insecticides being developed for management of beet armyworm and cabbage looper in lettuce and cole crops.

Product	Active Ingredient	Formulation Tested	Mode of Action	Primary Activity	Rates Tested a	Field Efficacy b
Alert	chlofenapyr	2 SC	metabolic	translaminar	0.10-0.15	BAW: excellent/CL: excellent
Success	spinosad	2 SC	neurotoxic	translaminar	0.09	BAW: excellent/CL: excellent
Proclaim	emamection	0.16 EC, 5 G	neurotoxic	translaminar	0.0075	BAW: excellent/CL: good
Confirm	tebufenozide	70 WSP, 2 F	hormone agonist	ingestion	0.06-0.125	BAW: excellent/CL: good
Avant	?	30 WDG	neurotoxic	ingestion	0.025-0.090	BAW: excellent/CL: excellent
Crymax	Bt 'kurstaki'	WDG	infection, septicemia	ingestion	1.0 lb. product	BAW: moderate/CL: excellent
Neemix	azadirachtin	4.5 EC	hormone agonist	ingestion, contact	1.0 pt. product	BAW: fair/CL: fair
Lannate	methomyl	SP, LV	neurotoxic	contact	0.6-0.75	commercial standard
Larvin	thiodicarb	80 DG, 3.2 EC	neurotoxic	ingestion	0.75	commercial standard

^arate/acre expressed as lbs. AI unless otherwise noted. ^befficacy compared to commercial standards: Excellent, >90% control after 5 days exposure in field; Moderate, 50-85% Fair, <50%.

Table 2. Insecticides being developed for leafminer in vegetables and cucurbits.

Product	Active Ingredient	Formulation Tested	Mode of Action	Primary Activity	Rates Tested/Application	Lifestage Activity	General Efficacy
Agrimek	abamectin	0.15 EC	neurotoxic	translaminar	0.009 (8 oz.)	larvae, adult suppression	commercial standard
Trigard	cyromazine	WSP	IGR	systemic	0.125	larvae	comparable to Agrimek
Neemix	azadirachtin	4.5 EC	IGR	ingestion, contact	1.0 pt. product	larvae-pupae	fair control
Success	spinosad	NAF 295 1.6 DE	neurotoxic	translaminar	0.09	larvae, adult suppression	comparable to Agrimek on L. sativa
Proclaim	emamectin	0.16 EC 5 G	neurotoxic	translaminar	0.0075	adult	marginal suppression
Alert	chlofenapyr	2 SC	metabolic	translaminar	0.10-0.15	adult	marginal suppression

Rates expressed as lbs(a.i.)/acre unless otherwise noted.

Table 3. New insecticides being developed for aphids in lettuce, cole crops, and spinach.

Product	Active Ingredient	Formulation Tested	Mode of Action	Primary Activity	Rates Tested/Application	General Efficacy
Admire	imidacloprid	2 F	neurotoxic	systemic-ingestion	0.25-0.32 soil incorp.	commercial standard; provides season-long protection
Provado	imidacloprid	1.6 F	neurotoxic	translaminar	0.05 foliar	comparable to Admire/repeated applications (7-14 d residual)
CGA 293343	nitro-methylene	2 SC	neurotoxic	translaminar	0.05-0.10 soil incorp.	comparable to Admire at planting
NI 25	acetamiprid	80 WP	neurotoxic	systemic-ingestion	0.5-0.075 foliar	comparable to Admire/repeated applications (7-14 d residual)
Fulfill	pymetrozine	40WP 50WP	anti-feedant	systemic-ingestion	0.06 foliar	comparable to Admire/repeated applications (7-14 d residual)
Aphistar	LRH-7988	50WP	neurotoxic	systemic-ingestion	0.10 foliar	comparable to Admire/repeated applications (7-14 d residual)

Rates expressed as lbs(a.i.)/acre unless otherwise noted.

Table 4. Insecticides being developed for potential control of thrips on lettuce.

Product	Active Ingredient	Formulation Tested	Mode of Action	Primary Activity	Rates Tested/Application	General Efficacy
Lannate+ Ammo	methomyl+cypermethrin	90S+2.5EC	neurotoxic	contact	0.75+0.1 foliar	commercial standard, 80-90% control 5-7 days
Dimethoate+Orthene	dimethoate+acephate	E267+75 S	neurotoxic	contact	0.25+0.75	comparable to Lannate/Ammo at 7 days
Fipronil	phenyl pyrazole	80 WDG	neurotoxic	contact, ingestion	0.05 foliar	comparable to Lannate/Ammo at 7 days
Success	spinosad	NAF 295	neurotoxic	translaminar	0.07-0.13 foliar	high rates comparable to Lannate/Ammo at 7 days

Rates expressed as lbs(a.i.)/acre unless otherwise noted.

This article was written by John Palumbo, University of Arizona, Yuma Ag. Center, and modified for publication in C.C.Ag. Highlights.

TOLERANCE OF VEGETABLE CROPS TO HALOSULFURON

There are few options for nutsedge control in most vegetable crops. Halosulfuron is a selective herbicide that we have found to be effective in controlling yellow and purple nutsedge. Several varieties of vegetables were tested for tolerance to pre-emergent treatments of halosulfuron. Tolerant crops included carrot and the warm-season crops: melon, snap bean, pepper, cucumber, squash, and okra. Most of the cool-season vegetables were intolerant of halosulfuron. The difference in tolerance between warm-season and cool-season crops has important management implications. Summer nutsedge control is the primary application for halosulfuron. Rotations of warm-season vegetables or field crops followed by cool-season vegetables are common in many vegetable producing regions. Soil carryover of halosulfuron could lead to crop injury when fields are subsequently planted to cool-season vegetables.

However, we found the current label restrictions for plant-back to be overly cautious. Current label restrictions do not permit the planting of many vegetables for 1-2 years. Our experiments found that waiting 6-12 months after applying halosulfuron would provide more than adequate safety. We recommend a reduction in the plant-back interval for halosulfuron.

Table 1. Tolerance of vegetable crops to halosulfuron. Injury ratings are based on visual observation using a scale of 0-10, where 0 equals no injury and 10 equals complete death of the plant. Means followed by the same letter are statistically equal.

Crop Species	Variety	Crop Injury @ 4 weeks	Crop Injury @ 6 weeks	Dry weight, as percentage of untreated
Carrots	Goldmine	0 j	0 l	94.91 ab
Lettuce	Paris Island	7.75 c	7.5 c	26.36 gh
Onions	Southport White Globe	7.5 c	6 e	21.48 h
Spinach	Bassanova	6.5 d	7.75 c	27.52 g
Melon	White Crenshaw	2.75 e	3 f	77.98 dc
Cantaloupe	Topmark	2.5 e	1.25 g	79.07 cd
Melon	Honeydew Green	.75 gh	1 h	83.28 cd
Green Bean	Strike	2 f	.75 l	79.42 cd
Bell Pepper	Keystone R. Giant	.25 ij	.25 k	83.56 c
Red Cabbage	Red Sun	8.75 a	8.75 a	4.44 i
Red Cabbage	Azzuro	8.25 b	8.75 a	4.42 i
Red Cabbage	Primero	8.25 b	8.25 b	5.1 i
Cucumber	Superset	1.75 f	.5 j	99.86 a
Cucumber	Celebrity	.5 hi	.25 k	48.51 f
Chinese Broccoli	N/A	8.75 a	8.75 a	3.37 i
Squash	Zuchlong	1 g	.5 j	97.61 ab
Squash	Prelude 2	.75 gh	.5 j	92.15 b
Okra	Clemson	2 f	.25 k	73.25 e
Lsd value at alpha .05	N/A	.273	.2187	5.513