Ontario Field Crop Report – June 22, 2022

Insect/Pest Update – Current Issues

Cereal leaf beetle (CLB) populations have reached threshold in some spring cereal fields this week (Figure 1). CLB larvae and adults feed on the tissue between leaf veins, leaving long scratch marks that can make plants appear silver or frosted from a distance. Before boot stage, the threshold is an average of three larvae per tiller. One CLB adult or larvae per stem warrants control after boot stage but prior to heading. Once headed, protecting from injury to the flag leaf is key in early heading stages. Control in early stages of heading is only warranted if CLB are still actively feeding directly on the flag leaf before the grain fill period (Zadok 75) is complete.

Thrip infestations have been spotted in a few corn fields again this year. Typically, not a pest of concern, thrips have become an annual problem for some corn, soybean and spring cereal fields in Ontario. These tiny cigar shaped insects feed on the underside of the leaves, leaving scars along the veins of the leaf (Figure 2). When young plants are stressed from lack of rain or a nutrient deficiency, thrips may thrive, moving beyond the lower leaves, causing feeding injury up to the newest leaves. No thresholds are available as typically the plants can grow ahead of the infestations. Control may only be warranted if infested fields continue to be significantly moisture stressed with no rain forecasted, and there are several thrips per leaf throughout the plant, but especially if thrips are causing injury on the newest leaves.

Potential Upcoming Pest Issues

Two-spotted spider mite (TSSM) populations in Ontario soybeans and dry beans are becoming tolerant to dimethoate (Lagon® or Cygon®). Despite last year’s field season not being ideal for TSSM, samples were collected in ten fields in southwestern Ontario that had reached threshold. Populations from these sites were found to be resistant to dimethoate. In a hot dry year, we expect to see significant problems in soybeans and dry beans. Through a collaborative research project with Western University, AAFC – London and OMAFRA, we hope to understand the distribution and extent of this resistance. Currently, dimethoate is the only active ingredient registered for spider mites in soybeans and dry beansis very concerning, and increases our need to test these spider mite populations to find what possible alternative products are still effective and can be registered to replace dimethoate. If you find any spider mite populations in soybeans or dry beans before an application is made (preferable), or after a dimethoate application that was not successful at controlling the population, please contact Tracey Baute (tracey.baute@ontario.ca). Spider mite samples will be submitted to Western University for resistance testing. Fields with a history of spider mite problems or fields close to greenhouse operations are of special interest, since they could influence which control products they have been previously exposed to.

Corn rootworm (CRW) populations could be heavy again this year, as Bt resistant populations continue to spread and new counties are identified with problem fields. Hot, dry conditions, like forecasted over these next few weeks, are ideal for adult activity.In continuous corn fields with repeated use of Bt rootworm hybrids, monitor for beetles in July and August. Those fields that had heavy CRW adult pressure last year will have experienced abundant egg laying in late summer. The larvae that hatched from those overwintered eggs are happy to find corn roots planted in those same fields again this year. Look for signs of lodging and goosenecking by digging up the roots to determine the extent of the root feeding. Contact your seed provider or Tracey Baute, OMAFRA if unexpected damage in Bt rootworm hybrids is found.

The Regional Corn Rootworm Trap Network will continue in 2022 and we are looking for more trap participants in Ontario. Trap sites in continuous corn with a history of repeated use of Bt rootworm hybrids are preferred trap sites. If you are interested in getting free trap supplies in Ontario, please contact Tracey Baute (tracey.baute@ontario.ca) so we can get traps to you before July when trapping will start. Trap supplies are free to growers and crop consultants thanks to funding from the Grain Farmers of Ontario (GFO) and the Agricultural Biotechnology Stewardship Technical Committee (ABSTC). Monitoring sticky traps weekly during adult activity helps us gain insight as to whether it is a bad rootworm year and alerts us to regions and fields where rootworm activity may need further scouting and monitoring for potential resistance issues. It is also improving our understanding of where both northern and western CRW populations are in Ontario and across North America.

Weather Data

Location & Year	Weekly June 13 – 19 2022			Accumulated
	Highest Temp (°C)	Lowest Temp (°C)	Rain (mm)	Rain (mm) April 1st	GDD 0C April 1st	GDD 5C April 1st	CHU May 1st
Harrow 2022	33.3	15.3	15.4	205	1021	669	961
Harrow 2021	28.7	8.8	12.8	143	1096	714	943
Harrow 10 YR Avg. (2011-20)	27.6	12.7	18.9	237	1065	668	998
Ridgetown 2022	33.7	11.8	3.3	174	951	606	874
Ridgetown 2021	27.1	5.5	13.4	135	1023	650	891
Ridgetown 10 YR Avg. (2011-20)	27.0	11.0	19.9	208	988	596	919
London 2022	32.0	8.9	0.4	181	924	583	841
London 2021	26.0	4.0	8.2	135	1021	652	864
London 10 YR Avg. (2011-20)	27.3	10.6	16.0	224	971	582	905
Brantford 2022	32.2	9.1	8.1	169	914	568	808
Brantford 2021	29.1	5.0	2.9	122	1001	631	852
Welland 2022	31.1	13.0	2.2	189	959	603	859
Welland 2021	28.2	5.7	8.1	93	992	619	839
Welland 10 YR Avg. (2011-20)	27.1	10.8	12.4	229	971	581	898
Elora 2022	30.2	7.4	0.0	163	841	508	742
Elora 2021	26.7	3.6	21.6	119	912	551	768
Elora 10 YR Avg. (2011-20)	25.9	9.2	13.8	222	853	478	784
Mount Forest 2022	31.2	6.9	0.0	179	850	523	770
Mount Forest 2021	25.5	3.9	1.3	102	921	563	778
Mount Forest 10 YR Avg. (2011-20)	25.3	8.9	18.0	211	837	469	777
Peterborough 2022	30.1	8.9	13.1	212	845	497	761
Peterborough 2021	27.5	3.7	15.3	106	902	531	760
Peterborough 10 YR Avg. (2011-20)	26.9	7.6	15.3	216	865	489	794
Kemptville 2022	29.5	10.4	0.6	272	923	555	835
Kemptville 2021	29.0	7.5	43.5	142	1012	635	840
Kemptville 10 YR Avg.  (2011-20)	27.5	9.4	13.4	217	903	529	838
Earlton 2022	28.8	10.2	15.5	159	737	439	725
Earlton 2021	30.3	3.8	4.7	84	858	506	711
Earlton 10 YR Avg. (2011-20)	24.8	6.6	17.7	180	655	364	647
Sudbury 2022	27.4	9.7	2.8	187	732	424	692
Sudbury 2021	26.0	4.5	14.9	135	859	509	722
Sudbury 10 YR Avg. (2011-20)	25.2	8.2	13.4	198	721	406	699
Thunder Bay 2022	22.4	8.1	6.2	308	537	266	485
Thunder Bay 2021	30.0	5.1	0.4	185	734	396	648
Thunder Bay 10 YR Avg. (2011-20)	23.6	5.5	21.3	185	594	290	542
Fort Frances 2022	24.1	12.0	28.4	329	586	317	578
Fort Frances 2021	27.9	5.0	3.0	145	799	455	745
Fort Frances 10 YR Avg. (2011-20)	23.6	7.1	27.5	189	689	367	660
Report compiled by OMAFRA using Environment Canada data. Data quality is verified but accuracy is not guaranteed. Report supplied for general information purposes only. An expanded report is available at www.fieldcropnews.com.

Crop Report – June 15, 2022

Soybean Update

Soybeans range from emergence (VE) to the fourth trifoliate leaf stage. The majority of the crop was planted in May, although sporadic showers meant that some fields could not be planted until June. A few soybeans were planted in April. They are now at the fifth trifoliate leaf stage. Ideally, soybeans should have 6 trifoliates by the time they begin to flower to maximize yield potential.

What is the Critical Weed Free Period?

Soybeans are susceptible to yield losses from weed competition, especially when they are small. The critical weed free period is the time during the growing season when uncontrolled weeds cause the greatest yield loss. Yield losses from the presence of living weeds during this time are irreversible. This makes early season weed control essential.

There are several factors that dictate the exact length of the critical weed free period, such as weed density, weed species, and when the weeds emerge. It’s well documented that if weeds are not controlled by the first trifoliate, yields will decline rapidly each day they are not sprayed. Studies have shown that beginning from the first trifoliate, uncontrolled weeds can reduce yield by 0.5 to 2 bu per acre per day. The first trifoliate to the third trifoliate growth stage is considered the “critical weed free period” since the presence of weeds during this time causes the highest yield losses. In wide rows or low plant populations, the weed free period is slightly longer.

The best strategy to reduce yield losses is to always start with a clean field at planting, either through tillage or an herbicide application. It’s important to know that weeds that emerge at the same time as the crop cause the greatest amount of competition and yield reduction, which is partly why many growers use a soil applied residual herbicide in addition to Roundup. Later emerging weeds have less of an impact on final yield. As a rule of thumb, the first in crop application should be made approximately 21-28 days after seeding.

Is it Too Late to Apply Potash?

Potassuim (K) and Manganese (Mn) deficiency are already evident this year. These two nutrient deficiencies have unique leaf symptoms. K deficient leaves turn yellow along the leaf margins (see Figure 1.), while Mn deficient leaves turn yellow across the whole leaf, except for the veins which remain green (see Figure 2.).

A soil test is the only reliable way to know if a field is truly low in K or if the plants are just showing stress-induced potassium deficiencies. K deficiency symptoms may also indicate soybean cyst nematode (SCN) feeding on the roots. If the soil test is poor for K (less than 100 ppm) a broadcast application at this time is still warranted as a remedial management strategy. Soybeans are very responsive to potash and have the ability to utilize surface applied potash even after planting.

Manganese Deficiency

One of the most significant factors affecting the availability of Mn is the soil pH. As soil pH increases, less Mn is available to the plant. The deficiency is most common on poorly drained soils, especially clays. The amount of air in the soil also impacts available Mn, so tire tracks often show less Mn deficiency. High organic matter also ties up Mn. Since Mn is a micronutrient, a foliar application of Mn works well to rectify the deficiency and can provide a 5+ yield response.

Replants

Many soybean fields are struggling this year to achieve a perfect stand. Keeping an existing stand is often more profitable than replanting at this date. The uniformity of the existing crop is more important than having a high population. Soybeans have an impressive ability to compensate for thin stands under good growing conditions. Soybean plants can fill spaces up to 30 cm (12 inches) within or between rows with relatively little yield reduction. Research has shown that a final stand of 90 000 plants per acre in 7.5-inch rows provides a yield potential of 90 percent. Plants must be healthy, evenly distributed and weed free for low populations to flourish. Field experience has shown that more plants per acre are needed on clay soils. A minimum stand of about 110 000 plants per acre on heavy clay soils is required to achieve good yields. When thickening a poor stand, use the same variety. These later planted seeds will mature within 10 days of the original stand even though they may have been seeded a month later in the spring.

Weather Data

Location & Year	Weekly June 6 – 12, 2022			Accumulated
	Highest Temp (°C)	Lowest Temp (°C)	Rain (mm)	Rain (mm) April 1st	GDD 0C April 1st	GDD 5C April 1st	CHU May 1st
Harrow 2022	27.4	11.4	33.1	189	924	592	844
Harrow 2021	29.8	12.8	6.3	130	956	610	772
Harrow 10 YR Avg. (2011-20)	25.9	12.1	15.7	218	923	561	822
Ridgetown 2022	25.9	9.3	42.1	170	859	534	765
Ridgetown 2021	29.2	11.1	7.1	122	897	559	740
Ridgetown 10 YR Avg. (2011-20)	25.6	11.0	9.1	188	855	497	755
London 2022	24.5	8.1	30.2	181	833	513	733
London 2021	30.4	12.6	7.8	127	898	565	717
London 10 YR Avg. (2011-20)	25.2	10.3	18.6	208	837	483	742
Brantford 2022	25.0	7.8	31.5	161	827	501	706
Brantford 2021	31.8	13.4	4.8	120	872	538	702
Welland 2022	26.2	10.1	41.0	186	876	540	758
Welland 2021	29.7	14.5	3.0	85	866	527	686
Welland 10 YR Avg. (2011-20)	25.0	9.8	20.8	216	838	483	736
Elora 2022	23.9	7.9	38.3	163	761	448	648
Elora 2021	31.3	12.3	3.3	97	793	468	628
Elora 10 YR Avg. (2011-20)	24.0	8.7	20.4	208	731	390	637
Mount Forest 2022	23.7	8.3	46.3	179	768	461	672
Mount Forest 2021	30.4	12.0	2.7	100	806	483	643
Mount Forest 10 YR Avg. (2011-20)	24.2	8.7	22.4	193	716	383	631
Peterborough 2022	22.9	6.9	80.6	199	769	441	672
Peterborough 2021	30.6	8.6	1.0	91	784	448	622
Peterborough 10 YR Avg. (2011-20)	24.7	7.8	26.2	201	744	403	652
Kemptville 2022	24.0	7.3	29.2	271	845	497	741
Kemptville 2021	32.0	9.6	0.6	98	888	545	693
Kemptville 10 YR Avg. (2011-20)	24.9	9.3	25.0	204	779	439	690
Earlton 2022	23.7	6.2	30.5	144	660	381	632
Earlton 2021	33.7	5.2	1.2	79	744	428	584
Earlton 10 YR Avg. (2011-20)	23.4	6.2	15.7	162	543	286	516
Sudbury 2022	23.1	7.9	46.2	184	658	371	604
Sudbury 2021	31.6	9.7	23.2	120	743	428	586
Sudbury 10 YR Avg. (2011-20)	23.2	8.0	12.7	185	601	322	557
Thunder Bay 2022	25.1	3.1	4.3	302	482	231	427
Thunder Bay 2021	31.5	4.1	29.8	185	615	312	511
Thunder Bay 10 YR Avg. (2011-20)	22.3	5.2	12.7	164	491	222	426
Fort Frances 2022	24.1	2.4	2.9	301	516	267	492
Fort Frances 2021	32.1	3.9	30.8	142	684	375	614
Fort Frances 10 YR Avg. (2011-20)	24.0	6.3	29.6	162	575	289	525
Report compiled by OMAFRA using Environment Canada data. Data quality is verified but accuracy is not guaranteed. Report supplied for general information purposes only. An expanded report is available at www.fieldcropnews.com.

GDD 0C – accumulated Growing Degree Days above 0 Degrees Celsius since April 1, 2022

GDD 5C – accumulated Growing Degree Days above 5 Degrees Celsius since April 1, 2022

CHU – Crop Heat Unit calculated from minimum and maximum temperatures since May 1, 2022