Page 9 - Aug242023
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PASTURE GRASSHOPPERS                                                                        The Midwest Cattleman · August 24, 2023 · P9

      By Dave Boxler, Nebraska Extension Educator
         Much  of  Nebraska  has                                                                              stem tissue and by cutting
      had several years of below                                                                              off leaves or stems.
      normal precipitation, which
      may allow grasshoppers to                                                                               Control
      become a problem.                                                                                          A grasshopper integrated
         The     2023      Rangeland                                                                          pest management (IPM) pro-
      Grasshopper Hazard Map                                                                                  gram called Reduced  Agent
      (Fig 1) indicates ten counties                                                                          and Area Treatment (RAAT)
      in Nebraska that had fall                                                                               was developed by research-
      adult grasshopper numbers                                                                               ers at the University of Wy-
      averaging over 15 per square                                                                            oming to improve grasshop-
      yard. These data are based on                                                                           per control in pastures and
      the 2022 adult survey, which                                                                            rangeland. This  chemical
      is a good indicator of possible                                                                         control strategy utilizes the
      grasshopper issues for the                                                                              insecticide Dimilin which
      summer of 2023. Economic                                                                                interferes with the molting
      thresholds for grasshopper                                                                              process of grasshoppers. Di-
      densities in rangeland vary                                                                             milin is applied in alternat-
      from 8 to 40 grasshoppers                                                                               ing strips, reducing applica-
      per square yard. The thresh-                                                                            tion costs by 50 to 60% and
      olds are influenced by sever-                                                                           reducing the amount of in-
      al factors, including the cost                                                                          secticide used by 65 to 70%,
      of control product, projected      Monitoring                            Approximately  50  species     compared to  conventional
      forage yield, and the value of        One of the better methods  of grasshoppers are found              broadcast  treatments. The
      forage considered for treat-       for determining grasshopper  on rangeland in Nebraska,               RAAT system provides up to
      ment.                              density is to count the num- though generally fewer than             85% control, depending upon
         Grasshoppers consume up         ber of grasshoppers using  10 species ever reach eco-                rate of growth of the forage,
      to 50% of their body weight        the square foot method. With  nomic levels, accounting for           the size of the grasshoppers
      every day in forage.  A rate       this method, sample at mul- 95  percent  of the damage.              and the coverage obtained.
      of just 2.7 grasshoppers per       tiple sites about 50 to 75 feet  Grasshoppers defoliate grass
      square yard equals 12,971          apart. Select a point sever- by direct feeding on leaf and
      grasshoppers per acre.  An         al feet away and visualize a
      acre with 69.7 grasshoppers        one-foot square area around
      per square yard equates to         the point.  Walk  toward the
      the consumption of forage by       point, counting any grass-
      one cow per day.                   hoppers you see in or jump-
         Pasture grasshopper spe-        ing out of this area. Repeat
      cies that are most damaging        18 times, total the number of
      are found in areas with less       grasshoppers, and divide by
      than 30 inches of annual           2. The resulting number will
      rainfall.  The western two-        be the number of grasshop-
      thirds of Nebraska fall into       pers per square yard.
      this  rainfall  category.  With
      the occurrence of consecutive      Life Cycle
      years of drought, grasshop-           The developmental stages
      per outbreaks are possible.        of all grasshoppers include
      The past several years south-      the egg, nymphal, and adult
      western, southcentral, and         stages. Most species overwin-
      western Nebraska has expe-         ter as eggs. Normally, grass-
      rienced below normal precip-       hopper eggs will remain in
      itation. This type of weather      the overwintering stage until
      pattern can play a large role      the    ground      temperature
      in rangeland grasshopper           reaches 50° to 55° Fahren-
      outbreaks, and monitoring          heit. Newly hatched grass-
      grasshopper numbers is im-         hoppers look like miniature
      portant to figuring out what       adults except they lack wings,
      action may be required.            and their sex organs are not
                                         developed.  As young grass-
                                         hoppers grow, they shed their
                                         skin (molt). Depending upon
                                         the species, they might molt
                                         four to six times, with five
                                         molts being the average. The
                                         rate at which nymphs devel-
                                         op is influenced by tempera-
                                         ture and food quality. Most
                                         species reach the adult stage,
                                         30 to 50 days after hatching.
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