Degree day accumulations for Kansas alfalfa weevils are well ahead of normal for the entire state this year (Table 1).  A similar trend occurred in 2024. As air temperatures continue to increase, it is recommended that scouting for weevil activity should be occurring right now in all regions of the state. There is a confirmed report of weevil activity in northeast Kansas.

Table 1. Alfalfa weevil degree days as of March 12, 2025.  Kansas Mesonet, 2025: Kansas Mesonet Alfalfa Weevil Degree Days Accessed 12 March 2025, http://mesonet.k-state.edu/agriculture/degreedays/

Accumulated Alfalfa Weevil Growing Degree Days
	Station	Actual	Normal	Departure
Northwest	Cheyenne	164	28	136
	Colby	165	25	140
Southwest	Garden City	236	59	178
	Meade	257	61	196
North-central	Hays	177	31	146
	Osborne	168	15	153
South-central	Hutchinson	190	35	158
	Harper	216	61	155
Northeast	Manhattan	135	27	108
	Corning	110	13	97
Southeast	Cherokee	197	55	142
	Woodson	180	41	139

Alfalfa weevil degree days are a great way to estimate what might be going on in the field and serve as a useful tool to know when to time scouting. Alfalfa weevil eggs begin hatching after 300 degree days have accumulated (Table 2).  Since we cannot determine if eggs present were laid the previous fall or the current spring, in Kansas, scouting should start after 180 degree days have accumulated starting from January 1.
 

Table 2. Approximate degree days required for alfalfa weevil development.  Excerpt from Whitworth et al., Alfalfa Weevils, Kansas State University, October 2022 (MF2999).

Degree Days or Thermal Units	Stage	Importance
25-300	Eggs hatch	In stems
301-450	1st and 2nd instars	Leaf pinholing – start sampling
450-600	2nd and 3rd instars	Defoliation
600-750	3rd and 4th instars	Defoliation
750+	Pupa to adult	Adults – some feeding – oversummering

Be aware of insecticide resistance

While warmer spring temperatures allow for faster alfalfa weevil development, be aware that dramatic temperature drops can slow down alfalfa growth, making the plants unable to keep up with feeding damage.  Treatment may be warranted in shorter fields between 3 and 7 inches tall when feeding is evident on the top inch of growth, and 1 to 2 larvae are present.  If a field is treated, it is important to verify that the expected amount of control was achieved.  In 2020, populations of alfalfa weevil resistant to lambda-cyhalothrin were verified in northwest and southwest Kansas and Oklahoma.  While this resistance has not appeared to become a widespread problem for Kansas producers, a couple of fields reported in central Kansas last year where lambda-cyhalothrin had reduced efficacy. Oklahoma continues to have resistance statewide.  Numerous products are available for alfalfa weevil control in Kansas (Table 3).  When making management decisions, it is important to rotate modes of action as this is an effective way to prevent the development of resistance. 
 

Table 3. Products registered in Kansas for control alfalfa weevil. Treatments listed are mainly used for treating alfalfa weevil larvae; products with an asterisk are also recommended for adult alfalfa weevil control. For more specific information relative to any insecticide, always refer to the actual label on the product.

Trade Name	Chemical Name	Mode of Action Class
Fastac CS	Alpha-cypermethrin	3A
Baythroid XL	Beta-cyfluthrin	3A
Lorsban	Chlorpyrifos	1B
Cobalt Advanced	Chlopyrifos + lambda-cyhalothrin	1B+3A
Stallion	Chlopyrifos + zeta-cypermethrin	1B+3A
Tombstone	Cyfluthrin	3A
Proaxis	Gamma-cyhalothrin	3A
Steward	Indoxacarb	22A
Warrior II w/Zeon Tech	Lambda-cyhalothrin	3A
Beseige	Lambda-cyhalothrin + chlorantraniliprole	3A+28
Lannate	Methomyl	1A
Imidan 70-W*	Phosmet	1B
Mustang MAXX	Zeta-cypermethrin	3A

For the most up-to-date alfalfa weevil degree day accumulations, visit the Kansas Mesonet Alfalfa Weevil Degree Day Calculator (https://mesonet.k-state.edu/agriculture/degreedays/).  For a complete guide to alfalfa weevil management recommendations, please refer to the upcoming 2025 Alfalfa Insect Pest Management Guide that will be available online soon.

Anthony Zukoff, Extension Entomology Associate – Garden City
azukoff@ksu.edu