From the Field – Agronomy Notes: Vol. 4, Num. 9

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August 7, 2020-

As we continue to assess the impacts of Hurricane Isaias, we wanted to share some additional management considerations that are focused to sucker control.
First and foremost, in a normal growing season most of our farmers in the east would probably be finished with sucker control chemical applications by now. Our current growing season has been filled with so many repeated issues, that some growers may be much as two to three weeks behind their normal crop schedule. Certainly, this statement doesn’t apply to everyone, but it’s reasonable.
What this means is that maleic hydrazide (MH) applications are probably delayed for these farmers. This situation could prove difficult because some buying companies have specific language in their contracts requiring that MH be applied after first harvest. In addition, the only practical sucker control application remaining for some of the leaning/windblown tobacco is an application of MH, because of its systemic properties. You’ll be reminded that contact (fatty alcohol) and flumetralin are contact local-systemics, which means they must physically touch a sucker to control it. One can imagine how difficult this is to accomplish when tobacco plants are leaning. MH is a true systemic, which means that once it is absorbed by the foliage, it is moved throughout the plant – predominantly to the most active growing points.
The conundrum we encounter in this situation is the balance that must be maintained between controlling suckers and reducing MH residues in/on cured leaves. Ultimately, this is a decision that must be made by a grower in communication with their buying company/companies. However, we have enough experience and data to provide the guidance necessary to assist both parties. The points that should be considered by farmers are below:
1.) Harvest Timing: most MH products have a 7 day PHI, so that interval must be followed to remain in compliance with federal regulations. However, I strongly argue that a grower should not spray MH if they will be stripping a field in the next 7 – 10 days. I just don’t think the reward of sucker control outweighs the risk of high residues in this scenario. In contrast, if harvest (either individual stalk position or stripping) will occur in more than 14 days, an application of MH is likely warranted. As always, we encourage growers to double check their MH labels to verify these requirements.
2.) Application Rate: We’ve made great strides in reducing the volume of MH applied to tobacco over the last 10-20 years. For example, our research has consistently shown that 1.50 lbs ai/acre works just as well as 2.25 to 3.0 lbs ai/acre (regardless of MH brand or formulation) (Tables 1 & 2). Here it is important to note that there are two MH formulations available to producers, 1.50 and 2.25 lbs ai/gallon. When considering these materials, the delivery of 1.50 lbs ai/acre would be 1 gal/acre and slightly less than 3 qt/acre, respectively. To dive into the data a bit, in Table 2, focus your attention to rows four through six. We concluded that 1.5 lbs ai/acre was as efficacious as 2.25 lbs ai/acre and that residues were generally lower in cutters and tips. Certainly, the results for tips are more conclusive than cutters but the trend is there. If you contrast that information with Table 2, you see that we achieved the same level of sucker control with 1.13 lbs ai/acre that we did with 2.25, 3.38, and 4.5 lbs ai/acre. We did not collect residue samples in the trials associated with Table 2, but we would expect residues to be lower with the smaller application rates. The take home message here is that growers can use a reduced rate of MH, relative to what was used in the past, without sacrificing product efficacy.
Table 1. Percent sucker control and MH residue in cutter and tip stalk position as influenced by systemic suckercide applicationa,b.
Treatment*

Sucker Control

 MH Residue-Cutter

MH Residue-Tip

%

__________________ppm__________________
1.5 GPA  MH (no flum.)

68 c

82 b

39 c
0.5 GPA  Flum. (no MH)

65 c

 —

—
0.5 GPA Flum. + 1.5 GPA MHc

90 a

 —

—
0.5 GPA Flum./1.5 GPA MHd

82 b

 157 a

93 a
0.5 GPA Flum./1.0 GPA MHd

82 b

   107 ab

66 b
0.5 GPA Flum./0.5 GPA MHd

69 c

  52 b

31 c
a Treatment means followed by the same letter within the same column are not significantly different.
b Systemic suckercides preceded by two applications of fatty alcohol at 4 and 5%, respectively.
c Flumetralin and MH tankmix application.
d Flumetralin and MH applied separately, 7 days apart.
*MH=1.50 lbs. ai/gallon formulation, GPA=gallons per acre
Table 2. Percent sucker control as influenced by various application rates of MH at two locations in 2014a,b.
MH Ratec

Sucker Control

 Yield Quality

Value
 

%

 Lbs/Acre

$/Acre

2.0 GPA

 96 a

 2,712 a 86 a

4,850 a
1.5 GPA

97 a

2,856 a

86 a

5,061 a
1.0 GPA

97 a

2,696 a

 85 a

4,672 a
0.5 GPA

89 a

 2,908 a

86 a

5,164 a
a Treatment means followed by the same letter within the same column are not significantly different.
b MH preceded by two fatty alcohol (4 and 5%) and a single flumetralin (0.5 gal/acre) application.
c MH=Royal MH-30 XTRA (2.25 lbs. ai/gallon), 1.5 and 2.0 gallons per acre are above recommended application rates.

3.) Solution Volume: This item may prove to be a little “out there”, as it’s not something we have discussed in the past nor is it likely something that many of us have considered in a number of years. Years ago, some of the original MH product labels recommended a total solution application volume of 35 gallons/acre. The logic behind this was that sucker pressure is greatest in the upper one-third of the tobacco plant and focusing MH application to that area is simply more efficient than running it down-stalk (from a plant physiology standpoint). This recommendation gradually faded away because it was more efficient, from an operating standpoint, to not have to change nozzle configurations on sprayers when growers were finished making applications of fatty alcohol and flumetralin. Simply stated, we could use 50 gallons of spray solution per acre for all of our sucker control applications, so why bother with changing to 35 for MH? Anyways, a reduced solution volume is something that a grower might consider doing in order to keep from saturating the lower stalk positions with MH. Certainly, this approach may concentrate MH residues in the upper-stalk, but it could prove beneficial for growers that are not stripping everything at once over a short amount of time. The agronomy team already had plans to address solution volume, so we should be able to answer this question by 2021 a bit more definitively

4.) Irrigation/Rainfall: we know that MH is very water soluble and that irrigation/rainfall is the ONLY way to realistically reduce cured leaf residues. Our rule of thumb is that we need time for MH absorption to occur in sufficient quantity through the foliage and after that, we’re ready for a wash-off. We like for MH to have about 10 hours of drying time before a wash-off event occurs. There’s no direct correlation that quantifies rainfall/irrigation totals with residue reduction, but we do know that as little as 0.5 inches of water can help in these circumstances. This may be the most difficult selling point, but if a grower can irrigate 24 hours after an application of MH, they are bound to be in a better situation than if they did not. Even better, if they can time the MH application 24 hours ahead of a rainfall, then we can let mother nature do some of the heavy lifting.
As always, if you have any questions, please contact your local Extension agent!
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