Malheur Experiment Station Information for Sustainable Agriculture

Four trials were conducted in 2000 to evaluate new herbicides for weed control efficacy and potato tolerance. These trials demonstrated that sulfentrazone (Spartan) at lower rates and flumioxazin (Valor) at all rates did not cause significant potato injury. Sulfentrazone and flumioxazin were highly effective in controlling redroot pigweed, common lambsquarters, hairy nightshade, and barnyardgrass when applied at the appropriate rates or in combination with certain herbicides. Sulfentrazone and flumioxazin represent a herbicide mode of action that is not currently used in potatoes and offer more effective hairy nightshade control than current herbicide programs. These products would benefit producers and this research will support efforts in obtaining registrations if the chemical manufacturers decide to pursue labels. Differences in hairy nightshade control with increased Matrix rates and various surfactants were not documented because of variable nightshade pressure. However, potato injury did not increase from either higher rates or the use of different surfactants with Matrix. Applications made when hairy nightshade plants are smaller may show advantages for some of the treatments investigated. Potato tolerance to high rates of dimethenamid-P and Dual II Magnum was documented, suggesting that rates typically used in production should pose little risk of injuring potatoes. A registration package for dimethenamid-P has been submitted to U.S. Environmental Protection Agency (EPA) and a label for use in potatoes should be approved in the next few years. The herbicide Select also was shown to effectively control volunteer barley in potatoes. Select would be a useful grass herbicide if it is registered for use in potatoes.

Four trials were conducted at the Malheur Experiment Station to evaluate new herbicides for weed control efficacy and crop tolerance in potatoes. All trials were sprinkler irrigated. Trials were planted April 19 in a silt loam soil with pH 7.0 and 1.6 percent organic matter (OM). 'Russet Burbank' seed pieces were planted every 9 inches in 36-inch-wide rows. Thimet 20G was applied at planting at a rate of 17.3 oz/1,000 ft of row. Experimental plots were four rows wide and 30 ft long. Plots were sidedressed with fertilizer (125 lb N, 10 lb Zn, 6 lb Mg, and 2 lb B/acre) on May 3 and beds were reshaped with a Lilliston on May 8. Preemergence herbicides were applied May 9 and immediately incorporated with overhead irrigation. Postemergence applications were made June 4. Treatments were applied with a CO₂-pressurized backpack sprayer delivering 20 gal/acre at 30 psi. Plots were irrigated with sprinklers according to crop requirements throughout the season. Potatoes were sprayed with Bravo and Dithane to prevent late blight and with sulfur dust to control powdery mildew. Potato injury and weed control were evaluated throughout the growing season and tuber yields were taken by harvesting the center two rows of each plot. Potatoes were harvested September 15, 18, and 19. Potatoes were graded for yield and size on September 22, 25, 26, 27, 28, and 29.

Potato Response and Weed Control with Sulfentrazone and Flumioxazin Combinations

Sulfentrazone was applied alone at rates from 0.125 to 0.375 lb ai/acre and at 0.188 lb ai/acre in combinations with other herbicides. Flumioxazin was applied alone at rates from 0.047 to 0.125 lb ai/acre and at 0.063 lb ai/acre in combination with other herbicides. Sulfentrazone and flumioxazin were applied in combinations with Eptam, Dual Magnum, Outlook, and Prowl. Sulfentrazone and flumioxazin treatments were compared to Sencor plus Matrix, Eptam plus Sencor, and Dual Magnum plus Sencor. Treatments were replicated four times.

Hairy Nightshade Control with Postemergence Matrix

This trial was conducted to evaluate various Matrix combinations for hairy nightshade control. To suppress other broadleaf weeds, all plots were treated with a preemergence application of Sencor (0.16 lb ai/acre). Matrix was applied at two rates (0.375 oz ai and 0.5 oz ai/acre) delayed preemergence (DPRE). Both rates were applied postemergence with either a non-ionic surfactant (NIS), crop oil concentrate (COC), or methylated seed oil (MSO). Delayed preemergence treatments were applied May 23 and postemergence treatments were applied on June 1. On June 1 hairy nightshade plants averaged 1.5 inches tall with an average density of 7 plants/ft². Treatments were replicated three times.

Tolerance of Russet Burbank Potatoes to Dimethenamid-P

This trial was conducted to evaluate preemergence dimethenamid-P for crop injury at normal field use rates and twice and four times the normal rate, and to compare it to other standard herbicides applied at twice their labeled rates. Dimethenamid-P is an active isomer of the herbicide Frontier (dimethenamid) and has been submitted to EPA for registration on potatoes. The proposed trade name for dimethenamid-P is "Outlook". Treatments were replicated four times. The untreated plots were hand weeded prior to row closure, but weeds emerging later in the season were not removed to avoid mechanical injury to the potato canopy. Lower yields in the untreated plots are likely due to weed competition.

Volunteer Barley Control with Select

Barley seed was broadcast over the entire trial and incorporated with the Lilliston on May 8. Prowl (0.75 lb ai/acre) was applied May 9 to control other weeds impacting the potatoes. Select treatments were applied May 24 when potatoes were 5 inches tall and barley had five leaves. Treatments were replicated three times. Potato injury and barley control were evaluated throughout the season. Because the Prowl application did not control all the broadleaf weeds, redroot pigweed and hairy nightshade control was evaluated at the end of the season.

Spring weather was conducive for early potato growth and the rapid canopy closure helped make soil active herbicide treatments effective. July and August were extremely hot, resulting in less than ideal conditions for potato growth.

Potato Response and Weed Control with Sulfentrazone and Flumioxazin Combinations

Sulfentrazone applied alone at the lowest rate (0.094 lb ia/acre) gave greater than 96 percent control of redroot pigweed, common lambsquarters, and hairy nightshade and 90 percent control of barnyardgrass (Table 1). The highest rate (0.25 lb ai/acre) gave complete control of all weeds, but also caused significant potato injury. Injury consisted of necrotic areas between veins on the leaves. Symptoms were not noticeable as the season progressed and injurious treatments did not reduce potato yield or quality (Table 2). Flumioxazin applied alone did not adequately control redroot pigweed or barnyardgrass. The lower rates were not as effective in controlling hairy nightshade. All the sulfentrazone treatments and flumioxazin alone at 0.094 lb ai/acre or higher or in combinations with Eptam, Dual Magnum, or Outlook provided greater hairy nightshade control than Sencor plus Matrix, Eptam plus Sencor, and Dual Magnum plus Sencor. The addition of Prowl to flumioxazin did not improve redroot pigweed or hairy nightshade control. Potato yields were strongly affected by weed competition, with treatments providing poor weed control resulting in lower potato yields. Flumioxazin will likely need to be applied in combination with other herbicides to provide acceptable control of a wide spectrum of weed species. Sulfentrazone rates likely can be reduced when applying it in combination with other herbicides.

Hairy Nightshade Control with Postemergence Matrix

All Matrix treatments provided hairy nightshade control, but differences between treatments were not observed (Table 3). This may be due to variable hairy nightshade populations in the trial. It was clear from this trial that potato yields are reduced when hairy nightshade is not controlled in potatoes (Table 4). Both marketable and total tuber yields were significantly lower in check treatment where hairy nightshade was not controlled compared to Matrix treatments.

Tolerance of Russet Burbank Potatoes to Dimethenamid-P

Higher rates of dimethenamid-P (1.29 and 2.58 lb ai/acre) and the highest rate of Dual II Magnum (5.2 lb ai/acre) caused significant stunting on May 19, but by June 13 no significant injury was apparent (Table 5). Even with the high levels of stunting observed initially, treatments did not reduce potato yields. Only the untreated plot had reduced marketable and total tuber yields compared to some of the other treatments. This was probably due to competition from weeds that were not removed from the untreated plots after canopy closure.

Volunteer Barley Control with Select

The preemergence application of Prowl did not control all broadleaf weeds in the trial. Select was very effective at controlling volunteer barley regardless of the rate and control was nearly complete for the entire season (Table 6). Because barley is so competitive, marketable potato yields were increased by more than 282 percent and the percentage of No. 1 by 369 percent with Select treatments (Table 7). The addition of Sencor to Select significantly increased control of redroot pigweed and hairy nightshade, resulting in higher yields than Select alone. Select would be a useful herbicide for controlling grasses in potatoes.

Table 1. Weed control and potato injury on June 1 with preemergence sulfentrazone and flumioxazin combinations. Malheur Experiment Station, Oregon State University, Ontario, OR, 2000.

Table 2. 'Russet Burbank' tuber yield and grade in response to preemergence sulfentrazone and flumioxazin combinations, Malheur Experiment Station, Oregon State University, Ontario, OR, 2000.

Table 3. Potato injury and hairy nightshade control with Matrix applications, Malheur Experiment Station, Oregon State University, Ontario, OR, 2000.

			Injury		Hairy nightshade control
Treatment	Rate	Timing	6-13		6-13	9-11
	oz ai/acre		--------------------------------------%--------------------------------------
Matrix	0.375	DPRE*	0		80	73
Matrix	0.5	DPRE	3		84	73
Matrix + NIS	0.375 + 0.25% v/v	POST	2		91	83
Matrix + COC	0.375 + 1.0% v/v	POST	3		86	68
Matrix + MSO	0.375 + 1.0 % v/v	POST	2		96	94
Matrix + NIS	0.5 + 0.25% v/v	POST	3		93	90
Matrix + COC	0.5 + 1.0% v/v	POST	2		85	67
Matrix + MSO	0.5 + 1.0 % v/v	POST	0		92	77
Matrix + Sencor + NIS	0.375 + 0.5 + 0.25% v/v	POST	7		90	79
Untreated			-		-	-
LSD (0.05)			NS		NS	NS

*DPRE = delayed preemergence.

Table 4. Tuber yield and quality in response to postemergence Matrix applications, Malheur Experiment Station, Oregon State University, Ontario, OR, 2000.

			U.S. No. 1					Total No. 2	Total marketable	Total yield
Treatment	Rate	Timing	4-6 oz	6-12 oz	>12 oz	Total	%
	oz ai/acre		---------------------cwt/acre------------------				%	-------------cwt/acre-------------
Matrix	0.375	DPRE*	83	262	105	449	76	76	526	594
Matrix	0.5	DPRE	92	267	74	433	75	57	489	577
Matrix + NIS	0.375 + 0.25% v/v	POST	89	268	98	455	75	68	522	602
Matrix + COC	0.375 + 1.0% v/v	POST	70	251	112	433	72	94	527	603
Matrix + MSO	0.375 + 1.0 % v/v	POST	90	235	99	433	70	90	514	609
Matrix + NIS	0.5 + 0.25% v/v	POST	75	253	108	437	73	82	518	596
Matrix + COC	0.5 + 1.0% v/v	POST	86	278	86	450	74	81	531	609
Matrix + MSO	0.5 + 1.0 % v/v	POST	80	287	84	451	77	56	506	584
Matrix + Sencor + NIS	0.375 + 0.5  + 0.25% v/v	POST	84	249	94	427	75	63	489	567
Untreated			94	228	30	352	75	32	383	470
LSD (0.05)			NS	32	NS	NS	NS	NS	66	57

*DPRE = delayed preemergence.

Table 5. Potato injury and yield in response to preemergence herbicides, Malheur Experiment Station, Oregon State University, Ontario, OR, 2000.

Injury

U.S. No. 1

Total

Treatment

Rate

Field rate

5-19

6-13

4-6 oz

6-12 oz

>12 oz

Total

%

U.S. No. 2s

Market- able

Yield

lb ai/acre

--------%---------

---------------------cwt/acre------------------

%

-------------cwt/acre------------

Dimethenamid-P	0.64	1X	2	4		84	262	71	452		76	73	525	599
Dimethenamid-P	1.29	2X	25	4		88	254	105	436		73	90	526	599
Dimethenamid-P	2.58	4X	31	9		71	232	95	397		67	126	523	591
Dual II Magnum	2.6	2X	3	5		82	249	95	424		73	70	494	580
Dual II Magnum	5.2	4X	26	8		65	239	93	390		66	125	516	590
Prowl	3.0	2X	1	10		62	260	86	457		72	116	573	636
Untreated	-	-	9	0		89	240	135	399		74	63	461	537
LSD (0.05)			14	NS		NS	NS	NS	NS		NS	NS	42	45

Table 6. Volunteer barley control with postemergence herbicides, Malheur Experiment Station, Oregon State University, Ontario, OR, 2000.

		Injury			Barley control				Redroot pigweed		Hairy nightshade
Treatment*	Rate	5-31	6-13		5-31	6-13	9-11		9-11		9-11
	lb ai/acre	-----------------------------------------------------%----------------------------------------------
Select + COC	0.125 + 1 qt	0	0		63	85	98		67		33
Select + COC + AMS	0.188 + 1 qt + 2.5 lb	3	0		67	96	99		63		37
Select + Sencor + COC	0.125 + 0.38 + 1 qt	5	0		67	91	100		99		70
Untreated		-	-		-	-	-		-		-
LSD (0.05)		NS	NS		NS	NS	NS		13		15

*COC = crop oil concentrate, AMS = ammonium sulfate.

Table 7. Potato yield in response to postemergence herbicide applications, Malheur Experiment Station, Oregon State University, Ontario, OR, 2000.

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Malheur Agricultural Experiment Station

Last updated  Tuesday July 30, 2002 .