Water Management to Minimize Pesticide Inputs in Cranberry Production (LNE94-050)

Water Management to Minimize Pesticide Inputs in Cranberry Production (LNE94-050)

Summary

Key Findings
This intensive study of the use of spring flooding to control pests and reduce chemical inputs in cranberry production began in 1995. This four-week flood, known as Late Water (LW), has been shown to suppress some insects, mites, and fungi, as well as stimulate plant growth. The study focused on comparing LW bogs with standard practice (EW) ones. Key findings include:
LW growers have been able to reduce the use of insecticides for early-season cutworms and especially for cranberry fruitworm (CFW) with no economic loss. LW reduced these populations in the year of the flood.
LW significantly reduced fruit rot incidence, allowing growers to significantly reduce fungicide use.
LW reduced dewberry, but was not effective on two other key weed pests.
This research confirmed that N use may be reduced by 30 to 30 percent in the LW year without impact on yield in the year of LW or in the following year.
On an LW bog, insecticide use can be reduced up to 60 percent, fungicide use can be reduced up to 50 percent, and nitrogen use is reduced 30 to 60 percent. Reductions vary depending on seasonal conditions.

Objectives
1. Determine the effect of LW on yield, flowering, vine growth, insect populations, disease incidence, and weed populations for the year of the LW flood and the following year.
2. Determine if the effects of LW on the plants and crop differ for the two major Massachusetts and New Jersey cultivars, Early Black and Howes.
3.Develop insecticide, fungicide, herbicide, and fertilizer use protocols as well as IPM monitoring protocols which would enhance the impacts of the LW flood for the year of LW and the following year.
4.Establish if LW can be used more often than one year in three thus further reducing pesticide inputs.
5.Investigate water quality of the LW flood: are pollutants being released in the flood water?
6.Conduct economic analysis: compare the cost of cranberry production using LW every three years to the cost of production without the use of LW.
7.Educate growers regarding the use of LW with an ultimate objective of increasing the use of this practice in the Massachusetts cranberry industry and introducing the practice in the Maine and New Jersey cranberry industries.

Recommendations
If possible, use LW every three years, though there are notable exceptions.
LW does not control all pests. If they are present in damaging numbers, treatments are timed based on trap catches.

Because fruitworm populations are typically strongly suppressed by LW, sprays should only be scheduled based on presence of eggs in sampled fruit.

Fungicide applications should be reduced in the year of LW and the following year. However, in the second year after LW, fungicide requirement increases.

Intensive glyphosate hand-wiping of dewberries after population reduction with LW may be economically feasible for eradicating this weed if the infestation level is low to moderate. Low rates of dichlobenil applied post-flood for dodder control do not harm cranberry plants.

Spring N application should be eliminated if a standard four-week LW flood is used. Mid season applications may be reduced, but overall N reduction should not exceed 40 percent or the following season crop may be affected.

Methods and Findings
One of the focus areas for this project was the possibility of adverse impact of LW on yield. This was the case in 1995, allowing us to define one of the conditions (abnormally warm preceding winter) that should preclude the use of LW in a given year. Note that in 1996 as in 1993 and 1994, LW had no adverse affect on yield. If yield reduction is minimized (or eliminated), cost savings due to fewer pesticide and fertilizer applications can offset any losses.

Progress has also been made in developing IPM and fertilizer protocols for LW bogs. We are: (1) investigating a pheromone-based monitoring system for late-season CFW infestations (currently, after LW, growers monitor by inspecting fruit for eggs) that will reduce grower labor and eliminate unnecessary late-season sprays; (2) looking for ways to reduce the cost of perennial weed management by integrating LW into an herbicide-wiping program, (3) determining whether fungicide use can also be reduced in the year following LW; and (4) defining the proper fertilizer practices for LW bogs so that excess growth is avoided without adverse impact on yield in the year after LW.

Specific Results
We studied the impact of LW on plant and pest populations at paired LW/EW sites in 1995 and 1996. We also assessed year-after-LW impacts on plants and diseases. In addition, we separated the plant impact and yield data for the two major cultivars: Early Black and Howes.

LW reduced the populations of early-season cutworms and cranberry fruitworm (CFW) in the year of the flood compared to those on EW bogs. The very low infestations on the LW bogs would have resulted in no recommended pesticide inputs for all but one of the LW locations. At 2 sites, sprays were applied in the middle of July targeting Sparganothis fruitworm, a pest not controlled by LW.

In both years of the study, LW bogs showed no significant increase in insect damage to fruit despite fewer insecticide applications.

LW significantly reduced fruit rot incidence allowing growers to significantly reduce fungicide use in the year of LW and in subsequent years with no increase in incidence of upright dieback disease. We found that LW changed the populations of the fungal pathogens which cause fruit rot in cranberries. Based on these results, it is now standard practice to reduce fungicide use in the year of LW.

LW reduced dewberry (Rubus hispidus) populations. In addition to reducing the number of viable crowns, LW reduced the vegetative spread of dewberries. LW did not reduce populations of two other key weed pests, glaucous greenbrier or Smilax glauca. Nor did LW reduce the germination of dodder (Cuscuta gronovii) seedlings.

LW bogs had fewer uprights and flowers per unit area then did EW bogs, and uprights tended to be longer. Despite having 25 percent fewer flowers than companion EW bogs, LW bogs had less than 10 percent lower yields in 1996. Increased fruit set may overcome decreased flower number. Vegetative uprights were longer or the same length on LW than on EW bogs despite significantly lower fertilizer use.

LW impact on yield may be severe if overall growing conditions are such that crops are generally poor. In 1995 and 1996, Massachusetts cranberry crops were reduced due to several weather factors including abnormally warm winter (1994-1995) and drought conditions (1995). Yield was not reduced by LW in 1993 or 1994. LW had a large adverse effect on yield in 1995 only.

Based on the comparison of two seasons of data, it appears that current standard IPM monitoring techniques should be used on all bogs. In most cases, early-season insecticide sprays for cutworms could be eliminated on LW bogs. However, it is important for an LW grower to continue scouting for CFW eggs even if none are found soon after fruit set. Populations may move back in from alternate hosts, the uplands, and adjacent EW bogs.

The number and rate of fungicide applications for fruit rot disease can be reduced during the first and second years after LW is used in addition to reductions (or elimination) in the year of LW. The data indicate that although a full fungicide schedule and fungicide rate are not required during the second year after late water, eliminating fungicides led to an increased incidence of fruit rot.

Even though LW floods reduce dewberry crown and runner fecundity, this single cultural practice is not sufficient to provide adequate economic control of this pest. Management must be multifaceted; the grower must be consistent and persistent in the application of any integrated program that targets dewberry.
Dichlobenil has been used on cranberry bogs as a pre-emergent herbicide to control the parasitic weed dodder. On bogs where dodder is a major problem, LW use may not be indicated. This is based on poor longevity of pre-flood casoron and dangers associated with post-flood applications (phytotoxicity), along with the fact that LW does not suppress dodder germination.

On LW bogs studied in 1995, growers reduced N use by about 70 percent, perhaps contibuting to the low yield on the 1995 LW study bogs. Those same bogs recovered some in 1996 but continued to have yields 20 percent lower than their previous five year averages. Clearly such drastic reductions in N fertilizer are not warranted despite the fact that plant growth appeared normal.

Water quality was studied in ten LW floods in 1995 and 11 LW floods in 1996. Based on this research, we recommend visual monitoring for algal growth and flood temperature monitoring if ambient
temperatures are high. Ideally, temperatures in LW should be elevated (60o-65oF) to kill CFW but higher temperatures may lead to adverse plant effects. Conversely, if temperatures remain low in the flood due to inflow (stream or pumping up flood level), insect control may be compromised.

Nutrients do not appear to be dispersing into the LW flood in significant amounts. Initial residues of dichlobenil in LW floods were highest on bogs that received 100 lb/A of the herbicide prior to the flood. There was some indication that application at least 7 days prior to the flood with adequate incorporation due to rainfall decreased the movement of the material into the flood. However, the major issue is efficacy rather than environmental impact as most of the initial residue has decayed by the time the flood is released.
Reported December 1997.